Christine Ohuruogu and Nicola Sanders ensured Britain will have two women in the World Championships 400m final for the first time in Osaka.
Ohuruogu produced an impressive semi-final performance
Ohuruogu continued her comeback from a year's ban for missing three out of competition doping tests, with a new personal best time of 50.17 seconds.
And Sanders also won her semi-final heat with a personal best of 49.77.
Britain's Phillips Idowu's hopes of a triple jump medal faded when he could only manage 17.09m, finishing sixth.
The 28-year-old had come into the finals recovering from a back injury and Idowu was not able to produce his best on the global stage once again.
"If I hadn't missed two months training it might have been different. I'm not distraught as I gave it my best shot," he told BBC Sport.
"I've been in the situation before when I haven't jumped for a couple of weeks and I have been able to put a big jump out. I tried man, I was working hard."
Idowu had gone to Japan as one of Britain's best hopes of winning an individual medal but his disappointment was made up for by the British runners on the track.
I'm really pleased but it's all about the final and this won't mean anything later
Sanders and Ohuruogu will contest their final on Wednesday, as will fellow Briton Andy Baddeley, who produced a late surge to qualify in fifth place for the men's 1500m final.
Jubilant one-lap runner Sanders said: "When I crossed the line I was shocked at my time.
"I'm really pleased but it's all about the final and this won't mean anything later."
Britain's other 400m semi-finalist, Lee McConnell, finished fifth in her heat in 51.07.
Baddeley looked well out of his semi-final as he went backwards down the back straight, but he reeled in the field on the home straight to reach the final in a time of three minutes 43.03 seconds.
"It wasn't a perfect run but it was my first World Championships, I'm in the final and I can't argue with that," he said.
The thrills continued in the men's 10,000m as Ethiopia's Kenenisa Bekele had to battle hard to wrap up his third straight crown.
Bekele raises his arms over the line to celebrate his third 10,000m gold
The 25-year-old's unbeaten streak over 10,000m looked to be coming to an end when compatriot Sileshi Sihine streaked away just after the bell.
But Bekele kicked past him round the final bend to claim gold in 27:05.90 from Sihine, while Kenya's Martin Irungu Mathathi took bronze.
Jamaica's Veronica Campbell had an agonising wait to find out that she was the winner of the women's 100m final.
The Olympic 200m champion crossed the line in 11.01 seconds - the same time as American defending champion Lauryn Williams, but was given the nod in a photo finish. American Carmelita Jeter was third.
"It was a nerve-wracking wait but it was a very close race and I didn't know who had won," Campbell told BBC Sport.
"I knew I had a good surge and I've been focused on gold, so I'm very happy."
Earlier, Britons Martyn Bernard and Tom Parsons produced personal bests of 2.29m to reach the high jump final, also on Wednesday.
Parsons, who was a last-minute entry in the squad, cleared the qualifying mark metres at his last attempt.
"To jump 2.29m is unbelievable and I am now starting to believe I belong here," said the 23-year-old.
The third Briton, Germaine Mason, fell short of the required height after managing only a solitary clearance of 2.19m while defending champion Yuiry Kryarenko also failed to go through.
Tasha Danvers-Smith also comfortably advanced to the 400m hurdles semi-finals in 55.67 seconds.
The Commonwealth Games silver medallist was more than a second down on her personal best but did enough to make sure she returns to the track on Tuesday.
American Tiffany Ross-Williams was the fastest qualifier in 54.24, while Australia's former world champion Jana Rawlinson, now married to former British hurdler Chris Rawlinson, also eased through.