LONDON - China's swimming star Sun Yang is looking to top the podium with a fastest time at Saturday morning's 400m freestyle heats as his strongest rival, South Korean Park Tae Hwan, lamented disqualification for false start.

Sun usurped the lead from the very beginning and was well ahead of his chasers, posting the fastest qualifying time at 3:45.07 to book a last-eight berth.

To everyone's surprise, defending Olympic champion Park was disqualified by a judge on the pool deck for a false start.

Park's jaw-dropping absence from evening's final wiped out a highly expected clash against Sun, who is seeking a revenge for his 400m freestyle losses to the South Korean at the 2011 Shanghai World Championships and the 2010 Guangzhou Asian Games.

"I'm very disappointed for Park and I was really looking forward to racing him in the final, and now that won't happen," said Sun, who has a clutch of world best times this year.

"As for me, I'm happy with my race," he added.

Park, who lost an appeal against disqualification, said: "I don't know why I was qualified. I will have to speak to my coach."

With Park's exit, the charismatic Sun is only one step away from becoming China's first Olympic men's swimming champion. He smashed Grant Hackett's decade-old 1,500m world record at the Shanghai worlds, and currently ranked world No 1 in the 400m, 800m and 1,500m freestyle.

The morning of Saturday also witnessed a good start for Chinese teenager Ye Shiwen, who clocked a second fastest time at 4:31.73 for a last-eight spot.

"I swam my best result because I have trained well. But I didn't feel at my best. The water is too cold," said Ye, world champion in the women's 200m individual medley.

"I wish I could win a medal but I would be happy with a personal best," said the 16-year-old, adding her top priority is the 200m individual medley.

Ye's teammate Li Xuanxu qualified fourth for the final of the women's 400m individual medley.

"I did quite well today. It's my best swim since we dumped the speed suit (bodysuit)," Li said.

"I didn't expect any medals tonight but I still want to swim as fast as I can," added Li, who will swim against triple Olympic champion Stephanie Rice and American world champion Elizabeth Beisel in the final.