NEW YORK - World No. 1 Victoria Azarenka and defending champion Samantha Stosur were among the fourth-round winners Sunday at the U.S. Open.

The top-seeded Azarenka was a straight-set victor over Anna Tatishvili at Louis Armstrong Stadium. The Belarusian, who won the Australian Open this year, defeated Tatishvili, 6-2, 6-2 to earn a date with Stosur in the quarterfinals of the final Grand Slam event of the year.

Stosur, seeded seventh, made quick work of 18-year-old British upstart Laura Robson with a 6-4, 6-4 triumph. The reigning U.S. Open champion fired six aces against Robson, who had already upset Kim Clijsters and Li Na.

In the nightcap, former world No. 1 Maria Sharapova overcame a 1-hour, 15- minute rain delay to dispatch Nadia Petrova 6-1, 4-6, 6-4. The third-seeded Sharapova has appeared in three of the last five major finals (1-2), including a French Open title run in June to complete a career Grand Slam.

Sharapova, a 2012 Olympic silver medalist and 2006 U.S. Open champion, will meet 11th-seeded Frenchwoman Marion Bartoli, who stormed back for a 1-6, 6-2, 6-0 victory over fifth-seeded left-handed Czech slugger Petra Kvitova.

Entering the match, Kvitova was a red-hot 15-1 since the Olympics, which included a recent win over Bartoli in Montreal.

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