LONDON - Ye Shiwen and Sun Yang seized gold on Saturday as China issued an emphatic challenge to US Olympic swimming supremacy on a day when American icon Michael Phelps floundered. Ye, 16, delivered a breathtaking closing freestyle leg to win the women's 400m individual medley in a world record of 4min 28.43sec.

Sun became the first Chinese man to win Olympic swimming gold as he denied South Korean Park Tae-Hwan a repeat of the 400m freestyle title he won in Beijing. Sun leapt onto a lane rope for a clenched-fist roar of celebration after winning in 3:40.14.

"It's beautiful," said a weeping Sun. "It's a big dream come true for me." He didn't apologize for his emotional reaction. Today, if I cry, it is because I have worked really hard in the last year, getting up early and training until late, so this makes it all worth while," Sun said.

Meanwhile, the highly anticipated duel between Phelps and team-mate Ryan Lochte in the men's 400m medley proved to be all Lochte as the laid-back Floridian won in 4:05.18 ahead of Brazilian Thiago Pereira and Japan's Kosuke Hagino with Phelps shockingly shut out of the medals in an event that figured in his eight-gold bonanza in Beijing.

Ye delivered a storming final freestyle leg to break the previous world record of 4:29.45, set by Australian Stephanie Rice en route to gold at the Beijing Games four years ago. "I dreamed of winning the gold medal, but I never ever expected to break a world record," Ye said. "I'm overwhelmed."

American Elizabeth Beisel, who led most of the way before Ye surged past her on the penultimate lap, was second in 4:31.27 and Li Xuanxu picked up a bronze for China for good measure in 4:32.91. Rice, nursing a shoulder injury, was tied for sixth. Sun, 20, swept past Park at the final turn and powered home, missing out on German Paul Biedermann's 2009 world record by seven-hundredths of a second.

"I didn't handle his comeback," admitted Park, who will now turn his attention to the 200m free beginning on Sunday. Sun, the 1500m freestyle world record holder, claimed a first international victory over Park, who made the final after a tumultuous day that included a disqualification for a false start in the heats and an appeal by South Korea that saw him reinstated.

"There was a lot going on for me this morning," Park said. "There was some influence from that in the final, but I am not going to blame it on that." That was just one of the oddities on a day when Phelps, who had never been seeded worse than fourth in an Olympic final, barely sneaked into the medley final and found himself swimming out in lane eight. Lochte won in 4min 05.18sec, comfortably in front of Brazilian Thiago Pereira in 4:08.86 with Japan's Kosuke Hagino claiming bronze with an Asian record of 4:08.94. Lochte said he was "in shock" and it could have been at finding himself atop the podium after taking bronze behind Phelps four years ago -- or at the absence of his illustrious teammate from the medals ceremony.

"I am really suprised Michael didn't medal," Lochte said. "Whenever he swims he is on the medal stand, no matter what." Phelps, fourth in 4:09.28, failed to medal in an Olympic final for the first time since 2000, when he swam just one race in Sydney as a 15-year-old.

In the interim, Phelps had won six gold and two bronze in Athens, and of course his vaunted eight golds in eight events in Beijing. "They swam a better race than me, they swam a smarter race than me and that is why they are on the podium," Phelps said. The flop denied Phelps in his first bid to become the first male swimmer to win the same event at three successive Olympics. He'll have a chance at trebles in the 100m and 200m butterfly and the 200m medley, but Japanese breaststroker Kosuke Kitajima kept his shot at the achievement alive with the sixth-fastest time in the semi-finals of the 100m breaststroke.

 Australia, long the Americans' greatest swimming rivals, won a dogfight for the 4x100m freestyle gold ahead of Beijing champions the Netherlands and the United States.

Alicia Coutts, Cate Campbell, Brittany Elmslie and Melanie Schlanger clocked an Olympic record of 3:33.15, just holding off a Dutch team of Inge Dekker, Marleen Veldhuis, Femke Heemskerk and rising freestyle sprint star Ranomi Kromowidjojo.

The Dutch took silver in 3:33.79 with the US quartet of Missy Franklin, Jessica Hardy, Lia Neal and Allison Schmitt earning bronze in 3:34.24.