MASON, Ohio (AP) -- Only one of the Williams sisters is heading to a semifinal, and it's not the one with the long winning streak. Serena Williams lost that - and her cool - at the Western & Southern Open.
Williams had her 19-match streak snapped by Germany's Angelique Kerber on Friday, the first time she'd even lost a set since Wimbledon.
Older sister Venus Williams reached the semifinals of a tournament for the first time this season by surviving her third three-set match of the week.
On the men's side, Novak Djokovic and Juan Martin del Potro won in straight sets, setting up a rematch of their bronze medal match at the Olympics. Del Potro won that one.
Roger Federer beat Mardy Fish to reach the semifinals, where he'll play Stanislas Wawrinka.