Stosur reaches fourth round; Li ousted at the Open

Reigning champion Samantha Stosur found her way into the fourth round, while former French Open winner Li Na suffered a third-round upset at the final Grand Slam event of the year -- the U.S. Open.

The seventh-seeded Stosur defeated 31st-seeded Uzbekistanian-born American Varvara Lepchenko 7-6 (7-5), 6-2 on a very hot day inside Ashe Stadium.

The Australian Stosur, who stunned American great Serena Williams in last year's finale in Flushing Meadows, will battle upstart British teenager Laura Robson on Sunday.

The ninth-seeded Li was knocked out by the rising Robson 6-4, 6-7 (5-7), 6-2 at Armstrong Stadium. The 18-year-old Robson beat a former major champion for the second time in two matches, as she ended the singles career of three-time U.S. Open champ Kim Clijsters here on Wednesday.

The talented Robson, the youngest woman in the top 100, is now into the fourth round at a major for the first time in her career.

Also on Day 5 at the USTA Billie Jean King National Tennis Center, 11th-seeded former Wimbledon runner-up Marion Bartoli handled fellow Frenchwoman Kristina Mladenovic 6-2, 6-4.

The 2012 women's singles champion in New York will earn at least $1.9 million.