Australia's world champion James Magnussen qualified fourth fastest for Tuesday night's Olympic 100m freestyle semi-finals in London.
Magnussen clocked 48.38 seconds as he finished second in his morning heat.
Magnussen was smiling after the swim and seemed to have regained some of his confidence after the disappointment of the 4x100m freestyle relay team's failure to win a medal in Sunday's final.
"The last couple of days have been some of the toughest of my life," he said.
"So I'm going to have to fight for this one but I'm willing to do it.
"I've learned more about myself in the past two days than I have in the past 20 years.
"If I can come back from this one I think it's a big achievement.
"The best thing for me is my coach and my support staff have shown confidence in me.
"We've sat down and talked a lot about it and about what we can do to fix those nerves and whatnot and I'm going to keep a positive outlook from now on."
American Nathan Adrian (48.19) topped qualifying while South African Gideon Louw (48.29) was second fastest ahead of Sebastiaan Verschuren (48.37), who just touched out Magnussen.
Australian James Roberts went through to the semis in 48.93, while 200m freestyle champion Yannick Agnel had the same time.
World record holder Cesar Cielo went through in 48.67.