Ranomi Kromowidjojo qualified fastest in the 50-meter freestyle preliminaries on Friday, keeping the Dutch swimmer on track to sweep the sprints at the London Olympics.
She touched in 24.51 seconds during the last morning of heats at the London Aquatics Centre. Kromowidjojo was back in the pool hours after winning the 100 free on Thursday for her country's first gold in the event since Inge de Bruijn won at the 2000 Games. De Bruijn swept the events in Sydney.
Dutch teammate Marleen Veldhuis was second-quickest in 24.57. Francesca Halsall had the British fans cheering loudly for her third-best time of 24.61.
''It was amazing walking out,'' Halsall said. ''The crowd were going mental. You smile because you want them to know you are enjoying it.''
Defending Olympic champion and world-record holder Britta Steffen of Germany was fourth in 24.70. She didn't advance to defend her title in the 100 free after sweeping the sprints at the 2008 Beijing Games.
Aliaksandra Herasimenia of Belarus, the silver medalist in the 100, was fifth at 24.76. Therese Alshammar, in her fifth Olympics at 34, moved on in sixth at 24.77. She had been in doubt about competing because of a pinched nerve in her neck.
''You want to have full movement, be able to move unrestricted and over the past two weeks I haven't been able to do that,'' she said. ''When you train a lot you want to be able to participate, so I'm happy I'm through.''
The Campbell sisters of Australia moved on after racing in the same heat. Bronte Campbell, two years younger than sister Cate, was ninth-quickest at 24.87.
''I have been racing her for years. She brings a bit of comfort and normality to it,'' Bronte said. ''She's like another swimmer but a bit louder.''
Cate, the bronze medalist four years ago in Beijing, tied for 10th with Sarah Sjostrom of Sweden at 24.94. She was surprised by her time and placement after being bothered by a stomach ailment.
''I've been lying on my back for the past two days,'' she said. ''I was happy to get out and swim.''
Jessica Hardy of the U.S. was 12th at 24.99. She is better known as a breaststroker, but she didn't qualify for London in either of those events.
''I've got my hands full,'' she said. ''I'm still green in this event. There's a lot of strong freestylers internationally.''
Her teammate, Kara Lynn Joyce, tied for 16th with two others and had to compete in a swim-off for the last spot in the evening semifinals. Amy Smith of Britain grabbed it in 24.82. Joyce was second in 25.16 and Sarah Blake Bateman of Israel was third at 26.03.
Sun Yang of China topped the 1,500 free heats in 14 minutes, 43.25 seconds. He set the world record of 14:34.14 in winning at last year's world championships in Shanghai.
Defending Olympic champion Ous Mellouli of Tunisia was second at 14:46.23. He will also compete in the 10-kilometer open water event at Hyde Park next week.
''I'm just happy I got the first race out of the way in these Olympics,'' he said. ''I've had some problems in my shoulder for the last two years and it seemed to be working pretty well this morning. I woke up this morning feeling mentally not very confident but the race went well.''
Ryan Cochrane of Canada, the bronze medalist in Beijing, advanced to Saturday's final in third at 14:49.31.
''Sun Yang is beatable and all of us are vying for that spot,'' he said.
Park Tae-hwan of South Korea was sixth, and Connor Jaeger of the U.S. advanced in seventh at 14:57.56, his second-best time ever. His teammate, Andrew Gemmell, was ninth and missed a spot in the eight-man final by 1.44 seconds.
The U.S. qualified first for the men's 4x100 medley relay, an event it has won at every Olympics since 1960, except when the country boycotted the 1980 Moscow Games. Nick Thoman, Eric Shanteau, Tyler McGill and Cullen Jones were timed in 3:32.65.
Michael Phelps will swim the final on Saturday night, giving him a chance to close out his career with his 22nd medal. He is already the most decorated Olympian ever.
Britain's team of Liam Tancock, Craig Benson, Michael Rock and Adam Brown generated the loudest cheers for advancing in second at 3:33.44. Japan was third and Australia fourth.
In the women's medley relay, Australia easily qualified first in 3:55.42 and will try to win the event for the third consecutive Olympics. Emily Seebohm, Leisel Jones, Alicia Coutts and Brittany Elmslie were 3.46 seconds faster than Japan, which moved on in second at 3:57.87. Denmark was third.
The U.S. squad of Rachel Bootsma, Breeja Larson, Claire Donahue and Hardy were fourth at 3:58.88. The Americans haven't won the medley since 2000.
