Fina World Championships
Date: 17 July-2 August (swimming from 26 July) Venue: Rome
Live/highlights on BBC Two, Red Button and BBC Sport website
Replay - Halsall wins 100m freestyle silver
Great Britain's Fran Halsall grabbed silver in the 100m freestyle on day six of the World Championships in Rome.
Halsall, whose medal was Britain's fifth at the meet, finished second behind Germany's Britta Steffen.
Steffen broke her own world record with a time of 52.07 seconds, Halsall clocked 52.87, while Australia's Libby Trickett was third in 52.93.
Aaron Peirsol of the United States won the men's 200m backstroke in another world record of 1:51.92.
It was one of six more on Friday, bringing the total for the championships so far to 35 with two days remaining.
Michael Phelps collected his third gold medal of the championships as part of the victorious US 4x200m freestyle relay squad, who shaved one-hundredth of a second off the previous world record of 6:58:56.
Lizzie Simmonds broke Gemma Spofforth's British record as both women booked spots in Saturday's 200m backstroke final, finishing first and second in their semi.
Simmonds, who was only 12th-fastest in the morning heats, qualified third-fastest in 2:07.21, while Spofforth, the 100m champion and world record-holder, qualified fifth-fastest.
Simmonds said: "I think after having a couple of days off you get a bit ropey, and have to blow the cobwebs away - and luckily I made it through to the semis.
"Then I thought 'I've got nothing to lose'. I wasn't in a middle lane so just thought I'll go out, give it my all and hope I can hold on. I wasn't aware I was going that fast until I got to the wall."
World record holder Kirsty Coventry of Zimbabwe advanced with the fastest time.
In the morning session, Rebecca Adlington and Joanne Jackson qualified for Saturday's 800m freestyle final.
World record holder Adlington and Jackson were the two fastest swimmers in the 800m freestyle heats in 8:20.53 and 8:20.8 respectively.
The 25-year-old Steffen also won gold in the 100m free at the Beijing Olympics last year, where she finished ahead of 2007 world champion Trickett and American Natalie Coughlin.
Trickett led at the halfway mark, but Steffen overtook her on the last leg. Nor could the Australian hold off the 19-year-old Halsall in the closing stages.
City of Liverpool's Halsall, 19, said: "When I finished I just couldn't stop giggling, I couldn't believe it.
"It was fantastic, it was an amazing race to be in. I don't know whether to laugh or to cry, I've just been giggling and tears have been coming out."
Veteran Peirsol smashed the previous record of 1:53.08 that he set at the US championships in Indianapolis on 11 July.
Japan's Ryosuke Irie was second in 1:52.51, and 2007 world champion Ryan Lochte of the United States was third in 1:53.82.
Lochte was back on the top of the rostrum later when he and 14-time Olympic champion Phelps led theUnited States to victory in the men's 4x200m freestyle relay in a new world record of 6:58.55, beating their previous best set in Beijing.
"I think I was kind of carried by my teammates tonight," Phelps said. "I was probably half a second slower than I wanted but those guys were able to take control and Lochte [who also claimed his third gold of the championships] swam well."
Russia finished second, Australia third with Great Britain in seventh.
Daniel Gyurta of Hungary won the men's 200m breaststroke final by a hundredth of a second over American Eric Shanteau. Gyurta clocked 2:07.64, Shanteau 2:07.65, while Lithuania's Giedrius Titenis was third in 2:07.80.
Another world record went in the women's 50m butterfly, where Sweden's Therese Alshammar posted a time of 25.07 in the second semi-final - moments after it had fallen to Marleen Veldhuis.
Veldhuis had clocked 25.28 in the first semi to lower her own mark of 25.33, set on 19 April in Amsterdam.
Britons Adam Brown and Simon Burnett failed to qualify from the 50m freestyle heats, Jemma Lowe and Ellen Gandy missed out in the 50m butterfly heats and Ian Hulme also failed to progress from the 100m butterfly preliminaries.