In the men's 200m individual medley, which is considered wide open after American superstar Michael Phelps decided not to swim in the event, Hungarian Laszlo Cseh topped the rankings with a time of 1:56.34, followed by American Eric Shanteau, who swam a 1:57.65.
Australian Leith Brodie and Brazilian Thiago Pereira both finished with a 1:57.66, while American Ryan Lochte had the next-fastest time going into the semi-finals with a 1:57.94.
In the men's 100m freestyle, David Walters led the field into the semi-finals with a time of 47.59 seconds, followed by Sweden's Stefan Nystrand, who was 0.07 seconds off the pace.
South African Lyndon Ferns and France's Alain Bernard, who is considered one of the favourites in this event, were third and fourth respectively.
Cesar Cielo Filho, who set a championship record of 47.09 as opening swimmer of the Brazilian 4x100m freestyle relay Sunday, qualified for the semi-finals with the eighth-fastest time.