NEW YORK (AP) - The U.S. Open is under way with Samantha Stosur beginning the defense of her title.

Stosur, seeded seventh, kicked off the tournament Monday, playing the day's first match in Arthur Ashe Stadium against 64th-ranked Petra Martic of Croatia.

Other players starting Monday include third-seeded Andy Murray of Britain, coming off his Olympic gold medal at the London Olympics. He faces Alex Bogomolov Jr. of Russia. Top-seeded Roger Federer plays American Donald Young in the night session.

Also playing in Ashe are No. 3 Maria Sharapova, against Melinda Czink of Hungary, and No. 23 Kim Clijsters, opening the final tournament of her career with a first-round match against American Victoria Duval.

Clijsters missed last year with an injury, but has won the tournament the past three times she's entered - in 2005, 2009 and 2010.