For all the talk of slow times with super-swimsuits now taboo, Cameron van der Burgh came within 0.23 seconds of breaking his world record in the semifinals of the 50m breaststroke at the World Championships in Shanghai.

Van der Burgh won bronze in the 100m breaststroke, but in the one-length sprint he is king.

Michael Phelps' rocky season took another turn for the worse yesterday when the 14-times Olympic gold medallist was stunned by US teammate Ryan Lochte in the 200m freestyle.

Phelps led over the first 100m until Lochte surged from third place to claim a narrow win in 1min 44.44sec, with defending champion Paul Biedermann of Germany third.

The result means Phelps, the Olympic champion and former world record-holder in the event, fails to regain the crown he lost to supersuit-wearing Biedermann two years ago.

"I think that if I was on the other side of the pool that race could have been played a little different," Phelps said. "I think I woke him up in the first 100 and he went with it.

"I can't complain. I'm bummed I didn't win. But at the same time, with what we've done over the last 18 months, I'm more than a second faster than I was last year and a second-and-a-half off my best time in a suit," he said.

He remains on course for a possible five gold medals in Shanghai.

A dead-heat during yesterday's 100m backstroke final netted France two gold medals. Camille Lacourt and Jeremy Stravins touched at the identical time of 52.76 to jointly claim top spot, with Ryosuke Irie nabbing bronze.

Van der Burgh, the world record-holder and defending champion, scorched the fastest time of the evening semis to touch in 26.90secs. His closest rivals were Felipe Da Silva of Brazil (26.95) and Norway's 100m breaststroke world champion, Alexander Dale Oen (27.33).

Van der Burgh will line up in tonight's final bidding to keep his world crown. The only other South African swimmer to have successfully defended a title is Roland Schoeman, who won the 50m butterfly in 2005 and 2007.

The only South African swimmer in a final yesterday was Wendy Trott, who finished sixth in the women's 1500m freestyle in 16min 06.02secs, slower than her 16:05.63 SA record, which she set in the heats.

Commonwealth Games hero Chad le Clos, swimming alongside Phelps, finished sixth in his 200m butterfly semifinal, but his 1:55.56 was good enough to see him go through to tonight's final.

Le Clos, who finished school only last year, is not expected to make the podium, but pundits believe he is a star for the future.

Heerden Herman and Mark Randall failed to progress beyond the men's 800m freestyle heats, their times ranking only 18th and 20th.

South Africa's Karin Prinsloo (50m backstroke), Darian Townsend (200m individual medley), Graham Moore and Gideon Moore (100m freestyle) are all in action in the heats this morning.