MASON, Ohio: Serena Williams lost her cool and her 19-match winning streak at the Western & Southern Open early this morning.

Sister Venus did much better, reaching the semi-finals for the first time this season. Venus got past reigning US Open champ Samantha Stosur 6-2, 6-7 (2), 6-4.

Serena fluffed routine shots while losing 6-4, 6-4 to German's Angelique Kerber. She hadn't lost a set since she won the title match at Wimbledon.

After losing a game in the second set, she threw her racquet at the ground, picked it up and slammed it on the court again.

No 9 Li Na beat Sweden's Johanna Larsson 6-2, 6-2.