The women's 400m medley relay final was scheduled for later Saturday.
Little more than an hour after her 50m butterfly performance, De Bruijn led the 50m freestyle semifinals in 24.75. Her world world record in the event is 24.13, set at the 2000 Sydney Olympics.
Germany's Thomas Rupprath (25.07) posted the fastest time in the 50m backstroke semifinals.
Lenny Krayzelburg, the American who holds the world record of 24.99 in the 50m back, is recovering from shoulder surgery and is not competing in these championships.
Luo Xuejuan of China (30.64) led the women's 50m breaststroke semifinals.
An estimated 12,100 fans attended Saturday night's races, the most of any session thus far in these championships.
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