Kelly Sotherton claimed Great Britain's first medal of the World Championships as she clinched heptathlon bronze.
The 30-year-old overhauled Austra Skujyte after finishing second in the closing 800m while team-mate Jessica Ennis settled for fourth overall.
Swede Carolina Kluft wrapped up a third world title ahead of Lyudmila Blonska.
American Tyson Gay claimed 100m gold in 9.85 seconds, leaving world record holder Asafa Powell to settle for bronze. Marlon Devonish came sixth.
LATEST ACTION (ALL TIMES BST):
To get involved, text us on 81111 (UK users only) or contribute to 606
1436: And we're going to leave it there for today - all back bright and early on Bank Holiday Monday then? Good. Phillips Idowu will be out to add to Britain's medal tally in the triple jump final while Ethiopia's Kenenisa Bekele goes for a third straight 10,000m title.
1433: And let's hear from the champion, Tyson Gay: "I've been working for this for a long time. I was real nervous but my mother was here and she calmed me down. It means a lot to me and I think the time will come later."
1430: Here's some words from Marlon Devonish: "It was always going to be a tall order to get on the podium but I'm gutted. I'm better than that. I felt comfortable in the rounds but just didn't come through at the end. I didn't panic, but maybe it was one race too many." He is distinctly a Brit down.
1425: Powell explains that he knocked his leg coming out of the blocks and that put him off his race. He tells BBC Sport: "I'm disappointed as I was the favourite to win but I lost the race. I made a big mistake and things like that do happen. I wouldn't say I cannot shine at the big occasions, it was just an unfortunate incident."
1421: It is all over in 9.85 seconds, and the winner is ... Tyson Gay. The American pulls back Asafa Powell after 60m and pours away to take his first major gold. Bahama's Derrick Atkins (9.91) takes a shock silver while Powell settles for bronze (9.96). Marlon Devonish finishes in sixth place in 10.14 - way below his personal best of 10.06.
1417: The sprinters are being introduced on the start line, and Powell looks pretty focused while Devonish in lane seven is pacing about.
1415: We're just five minutes away now and the BBC pundits are scoring it 2-1 in favour of Powell. MJ is sticking with Gay but Crammie and Colin Jackson are predicting a Powell win.
1405: "Marlon Devonish's mind-set must be 'I have every reason to be confident that I can run my best ever race now; the track is fast and I'm running against the best in the world'. He has every reason to believe it's possible. On the otherhand, it will be difficult for him, as Marc Burns and Derrick Atkins will also be chasing the bronze."
BBC pundit and five-time Olympic medallist Michael Johnson
1405: There is a glimpse of the 100m finalists in the call room. Asafa Powell is pacing up and down but looks pretty relaxed. Tyson Gay is sitting on the bench sticking on his numbers while Marlon Devonish sits, then stands. The pressure is building.
1400: The men's 400m hurdles semi-finals are in full swing on the track - though let's be honest we're all waiting for the men's 100m showdown. There was a bit of an upset in the second heat though as defending champion Bershawn "Batman" Jackson started tiring and clattered the last hurdle. He is out.
Poland's Marek Plawgo claimed the first heat in 48.18 seconds from American James Carter. On the comeback trail, Olympic champion Felix Sanchez wins the second in 48.32 from Perklis Iakovakis.
1348: In case you missed it, Great Britain have won their first medal as Kelly Sotherton clinches heptathlon bronze. The 30-year-old beat Skujyte, who was in third, by almost 12 seconds in the 800m to climb above her to bronze, while Ennis finishes fourth overall. Carolina Kluft takes gold with a points total of 7032 ahead of Lyudmila Blonska (6832) and Sotherton (6510). Ennis, 21, claims a new personal best points total of 6469.
Sotherton tells BBC Sport: "I wanted the medal so much, especially after such a poor start to the year, and I put in a lot of hard graft."
Ennis says: "This is my first Worlds and to come fourth is fantastic."
And Kluft says: "It's been a great competition and I couldn't ask for more. It's been a big pressure on me and I vowed to keep it all together, and now I have my third world title."
1340: That's it. Kelly Sotherton takes the bronze for Great Britain - the first medal of the championships. Now, three-time world champion Carolina Kluft leads the heptathletes on the traditional multi-event lap of honour.
1338: Sotherton leads at the bell with Jessica Ennis in second. On the back straight, Ennis moves into the lead and Sotherton who had slipped back to third is dragged back into it. Ennis wins in 2:11.40 and is followed home by Sotherton - looks like she has done enough to take the bronze.
1337: They are off in the 800m and Sotherton goes straight into the lead and Skujyte is off the back already.
1334: "Kelly will go into this event really confident as she knows she can run faster than Skujyte. Standing there I believe Kelly will run a smart race. She knows what she needs to do - and I believe she'll do it."
Former Olympic heptathlon champion Denise Lewis
And we're just about ready to find out ...
1325: "Time and time again, Mark Lewis-Francis has spectacularly failed to shine. There are only so many times you can listen to reasons why someone with such undoubted potential years ago is consistently failing to realise it."
Tabithakitten99 on 606
1315: Let's have a little breather before the heptathlon 800m - the last event. We are likely to be put through the wringer so here's a chance to catch our breath. If Kelly Sotherton can snatch bronze from Austra Skujyte, she has to beat the Lithuanian by around 2.5 seconds. The good news is that on paper she is much faster than that. Jessica Ennis is about six seconds adrift of Sotherton's pace. So it's fingers crossed.
1310: There's also some pole vault qualifying going on in Osaka. Britain's Kate Dennison cleared 4.20m but fails all attempts at 4.35m. The qualifying mark is 4.55m, or the best 12 qualified. And there is no surprise that world record holder Yelena Isinbayeva has not even bothered getting her pole out yet.
1304: A disappointing run for British champion Jeanette Kwayke in the last 100m quarter-final as she crosses the line in sixth. The heat was won by Chandra Sturrup in 11.15 from the defending champion American Lauryn Williams. Kwayke tells BBC Sport: "The positives are that I'm still learning but it's not good enough."
1300: A bit of drama over in the shot put as New Zealand's Valerie Vili snatches gold with her very last throw. She whacks out 20.54m - the longest throw in the world this year - and the defending champion Nadzeya Ostapchuk is relegated to second with German Nadine Kleinert third.
1255: There is no place in the 100m semi-finals for Britain's Montell Douglas who comes home sixth, in the third quarter-final which is won by Christine Arron in 11.17. The Frenchwoman sports a gingery-blonde hair-do and draws this comment from Steve Cram: "We've seen her with various hair styles over the years and this is not one of her best."
1250: Out on the track the women's 100m quarter-finals are already under way. There are two disqualifications in the second heat for false starts which vastly improves Britain's Laura Turner's chances of going through. And Turner does go through to Monday's semi-finals in 11.32. The Olympic 200m champion Veronica Campbell wins the heat in 11.08.
Turner tells the BBC: "I'm in the semi-finals but the time was rubbish. I'll be fresh tomorrow and get the adrenalin going."
1244: Bit busy at the minute but let's have a quick look at the women's shot put final. Defending champion Nadzeya Ostapchuk leads after landing 20.04m from New Zealand's Valerie Vili.
1240: "Sotherton is going to win a medal and hopefully there's more to come."
Roomurrhamil on 606
1230: Kelly Sotherton can only manage a season's best of 31.90m in the pesky javelin and so slides back to fourth overall in the heptathlon. Jessica Ennis lands another personal best of 38.07m and is in fifth. There's just the 800m to go. Can Sotherton haul herself up to bronze? The Briton is 37 points adrift of Lithuania's Austra Skujyte who has the bronze for now.
"There was nothing to lose on the last throw so she just had to hit it, but Sotherton is the fastest athlete in the 800m so she will just have to go out and run it."
Former Olympic champion Denise Lewis
1220: Tyson Gay wins the second heat in 10.00 ahead of Britain's Marlon Devonish. So the British number one goes through in 10.12 but Mark Lewis-Francis just misses out on a place in the final, as he is fifth.
"He doesn't panic Marlon. He knows he is good enough to get to the final. He has to go flat out but it is a good performance from him - and he still has an opportunity."
BBC commentator Steve Cram
1210: Derrick Atkins wins the first semi in 10.04 while Asafa Powell relaxes across the line in second, with his head turned to the side in total nonchalance. Craig Pickering comes home sixth in 10.29. Matic Osovnikar and Marc Burns also go through.
"Powell eased off in the last few strides. I thought we might have seen something a little quicker from him. Is the tension getting to him now? As for Pickering, he was run out of it."
BBC commentator Steve Cram
1210: Hmmm Pickering might have been too over-excited as he has false-started.
1208: Close to the men's 100m semi-finals now and Britain's Craig Pickering is really psyching himself up as he goes in the first heat alongside Asafa Powell. Lots of gesticulating and talking from the young Brit.
1200: Some field action to update you on. Carolina Kluft added to her points total in the heptathlon with a season's best throw of 47.98m in the javelin. In the second pool, Kelly Sotherton and Jessica Ennis have had their first attempts. Sotherton looks a little shaky as she lands 30.59m - a season's best - while Ennis lands 35.05m.
"Sotherton's body language is of someone who doesn't know what she is doing. She is thinking too much about it and the fear is inhibiting her."
Former Olympic champion Denise Lewis
The women's shot put final and pole vault qualifying is also under way.
1155: Jenny Meadows moves through a first lap well and unleashes a strong finish to come home in fifth. She won't go through but it's another personal best of 1:59.39. So none of the Britons make it through to Tuesday's final but it was a very tough ask for a group of good athletes who are still on their way up to world class.
1145: Marilyn Okoro, wearing lime green nail varnish, goes round the first lap in fourth. She comes up the home straight in second but just cannot hold on and gets overtaken by Mayte Martinez and Amina Ait Hammou to finish in fourth. There is some consolation as she gets a personal best of 1:59.63. But it's still 0/3 for the Brits.
"Okoro was impressive, powerful and acquitted herself so well. She was very unlucky and after another winter's training, she could be in the final in Beijing."
BBC analyst Brendan Foster
1135: First track action of the day and it's the women's 800m semi-finals, where three Britons are in action. Jemma Simpson decides to sit at the back of the group through the first lap and she is run out of it into sixth. So that's 0/3 so far. Belarussian Sviatlana Usovich wins the first heat in a personal best of 1:58.11.
1130: The men's 100m semi-finals get under way at 1210 and over at the warm-up track Asafa Powell is still looking relaxed, wearing a yellow Jamaica t-shirt and chatting to some of his team-mates. In contrast, Tyson Gay is sat on the track alone listening to his iPod. What can we glean from that?
1118: "I'm backing Asafa Powell to take the 100m after his Commonwealth Games victory last year. I hope Marlon Devonish can secure the bronze - but it's hard to judge the times going in from the second round, because some athletes were obviously holding back."
Mikesiva on 606
1104: Thoughts are already turning to the 100m final at 1420 BST; here's what MJ reckons:
"I don't think Powell is a great competitor and when it comes to the 100m it is like a heavyweight fight and you have to be a competitor too and withstand the pressure."
BBC pundit and five-time Olympic gold medallist Michael Johnson
1100: Sotherton and Ennis have already been out and about at the Nagai stadium contesting the long jump. Sotherton cemented her third place with a personal best leap of 6.68m, while Ennis was seven centimetres short of her personal best with 6.33m. Ennis, 21, - nicknamed Tadpole by Sotherton - is now 160 points behind her British team-mate.
1045: It is Konichiwa to another day in Osaka and it should be a cracking day of action.
Britons Kelly Sotherton and Jessica Ennis have two events left in the heptathlon; the javelin and 800m.
Sotherton's medal chances have been undone by the javelin before - she slid from second to seventh at last summer's Europeans - but can she do better in Japan?
The Olympic bronze medallist is in third with team-mate Ennis fourth, while Carolina Kluft looks to be on an unstoppable course for gold.
Marlon Devonish has been looking pretty relaxed out in the 100m rounds so far, and he will be aiming to at the very least reach the final. But can he sneak a bronze medal too?
The favourites to take gold and silver are, of course, world number one Tyson Gay and world record holder Asafa Powell. But which way will the medals be split?
I'm ridiculously excited about this already. Can you contain your own excitement? Let me know on 606.