Sarah Sjoestrom of Sweden has set a world record in the semifinals of the 100-butterfly at the world swimming championships. Competing in the second semi on Sunday night, Sjoestrom won in 55.74 seconds. She broke the mark of 55.98 set by American Dana Vollmer at the 2012 London Olympics. The final is Monday night at Kazan Arena. Copyright 2015 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.