Barcelona - Olympic champions Chad le Clos and Roland Schoeman on Friday qualified for their respective finals at the 15th FINA world championships in Barcelona.
Le Clos qualified for the finals of the 100m butterfly event with the second-fastest time, swimming a 51.52 - just 0.04 seconds behind American Ryan Lochte.
"I am happy, but there will be a lot of guys out there, who can go in the low. So we will see," said Le Clos.
"I had to work really hard tonight. Lochte was very good, especially after winning gold in the backstroke earlier in the session. It will be a big race, all the favourites are there.
"I am very excited to swim against Lochte. He is a good racer, so we will see tomorrow, it will be hectic," said Le Clos.
Veteran sprinter Roland Schoeman set back the clock as he qualified for the 50m freestyle final - 12 years after first medalling in the event in Fukuoka in Japan.
He won bronze and four years later won gold in the event in Montreal.
To crown his swim, the 2004 Olympic 4x100m freestyle champion equalled his own South African record of 21.67 - a time that saw him qualify in seventh place for Saturday's final.
He said that even though people had told him to retire, he had dismissed the idea.
"The idea is to make finals, I am really happy," said Schoeman.
"There have been a lot of set-backs in my life and a lot of times were I have fallen, but I am governed by integrity and the ability to bounce back.
"If I fail 100 times, I will get up again and nobody is going to stop me and that is a great thing for me.
"I felt way better than this morning. I think I can squeeze 0.20 out of the race. My last 10 metres can be way better than they were tonight.
"When you make the final anything can happen. I have just proven to myself I am on the right track. Tomorrow I will race for another medal for South Africa."
The Pretoria-born swimmer said he was proud that he had equalled his South African record which he set five years ago in Beijing.
In the women's 200m backstroke Karin Prinsloo came agonisingly close to breaking Melissa Corfe's South African record. The 24-year-old improved her time from the heats by 0.67 seconds, but was slower than Corfe by 0.01 second - the narrowest of times that is used to separate swimmers.
Prinsloo swam a 2:10.04 and finished tenth overall - 3.58 behind American Missy Franklin, who topped the qualifiers.
"It was a personal best, so it is fine. I am happy that I am already higher ranked than I was last year," said Prinsloo.