London - Olympic gold medallist Chad le Clos marched to his fifth final at the London Games when he broke the South African record for the second time.

He posted a time of 51.42 seconds in the semi-final of the men's 100m butterfly on Thursday night.

Le Clos broke Lyndon Ferns' South African record in the heats on Thursday morning with a time of 51.54 seconds.

“I'm very happy, obviously. This morning was a bit of a shock to me to go as fast and tonight was another great night for me. I took off another 0.1 of a second,” Le Clos said.

“I was so nervous coming down the first 50m... I was a second behind everyone. Thankfully I got a good turn and a good finish again.”

The 20-year-old South African, who won gold in the men's 200m butterfly on Tuesday, withdrew from Thursday's 100m individual medley final.

American Michael Phelps, the silver medallist behind Le Clos in the 200m final, swam the fastest time of the semi-finals, posting a time of 50.86.

Meanwhile, three-time Olympic medallist Roland Schoeman, swimming in his fourth games, advanced to the finals of the men's 50m.

Schoeman, who won the bronze medal in the same event at the Athens Games in 2004, finished fourth in his semi-final in 21.88.

“My goal was to make the final and I did that. I didn't have the greatest start by any means, so it's going to be good to get a rest and try to take it tomorrow night.”

His countryman Gideon Louw, however, failed to make the cut in his semi-final, which included defending Olympic champion Cesar Cielo, from Brazil.

Louw finished fifth with a time of 21.94.

Suzaan van Biljon, the only South African woman to make it into a final, finished seventh in the women's 200m breaststroke with a time of 2:23.72.

Van Biljon broke Penny Heyns' 13-year-old South African record of 2:23.64 in the semi-final on Wednesday.

“I'm really happy I exceeded my expectations with my time of last night (Wednesday),” Van Biljon said.

“My coach and I spoke afterwards and he said even if I go five seconds slower tonight, what I did last night was the goal.

“I'm really happy and it put the desire and motivation back to work hard and achieve something in my swimming again.”

She swam in the same race as America's Rebecca Soni, who broke the world record for the second night in a row.

Soni improved the world record in her semi-final on Wednesday to 2:20.00 and took a hundredth of a second off the time in the final.

Karin Prinsloo, swimming at her first Olympics, could not advance past the semi-final of the women's 200m backstroke.

She finished eighth in a time of 2:11.42. - Sapa