Chad le Clos believed he would need to swim faster than the national record he set on Monday if he wanted to win a medal in the men's 200 metres butterfly event at the London Olympic Games.

The versatile South African swimmer progressed to Tuesday night's final in style as he clocked a national record of one minute, 54.34 second (1:54.34).

"I definitely think I need to go faster if I want to win a medal," Le Clos said.

"I'm pretty sure that there will be at least three or four guys that could go under 1:54."

He finished second behind Takeshi Matsuda of Japan in the faster of two semifinals on Monday, while American Michael Phelps won the other semifinal in 1:54.53.

Le Clos hoped to replicate his performance in the semifinal in an effort to secure South Africa's second medal at the London Games.

"I'm going to go out there and make sure I am in the race and hopefully we'll have a race in the last 25 metres. It should be good."

Improving his personal best had given him a boost ahead of the final.

"I'm happy I broke my PB by almost a second," Le Clos said.

"That is the main thing for me, coming in here and getting my times down and proving to myself that I can handle the big stage."

The 20-year-old finished fifth in the men's 400m individual medley, his maiden Olympic final, on Saturday.

"To make the final was vital and I didn't expect to come top five, but that is an even bigger boost," he said.

"I think that helped me for this race (the butterfly semifinal)."

Le Clos, tipped to win a medal on his Olympic debut, believed he had an opportunity secure a podium place in the 200m butterfly final – perhaps his best event.

"I could come eighth or I could get a medal," he said.

"It is a very close final and there are some really great swimmers out there.

"I'm just going to go out there and I will race 100 per cent.

"When I finish that race I will be broke, I will give it my all and I guess you can't ask for more than that."