MIAMI, Fla. -- Top-seeded Caroline Wozniacki of Denmark and fourth-seeded Samantha Stosur of Australia were fourth-round losers Monday at the Sony Ericsson Open.
Germany's Andrea Petkovic knocked off Wozniacki with a 7-5, 3-6, 6-3 decision, while 16th-seeded Maria Sharapova eased past Stosur with a dominating 6-4, 6-1 triumph.
Wozniacki, the current top-ranked women's player, had reached the final in each of her last three events. She won in Dubai and Indian Wells, sandwiched around a loss to Vera Zvonareva in the title match at Qatar.
Petkovic is having a solid 2011 season. She lost to Petra Kvitova in the final of the Australian Open tuneup in Brisbane to start the year, then reached the quarterfinals of the year's first Grand Slam event with wins over Venus Williams and Sharapova -- the former via Williams' injury retirement.
Up next for Petkovic in the quarterfinals will be the winner between Jelena Jankovic and Anabel Medina Garrigues.
Stosur has had a rough start to her year. She was a third-round loser at the Australian Open and has reached the quarterfinals just once in her six events this year -- a loss to Jankovic in Dubai.
Sharapova, who lost to Wozniacki in the semifinals at Indian Wells last week, will next take on Romania's Alexandra Dulgheru, who advanced to the quarterfinals with a 6-3, 6-4 win over China's Peng Shuai.
Also scheduled for fourth-round play on Monday is second-seeded Kim Clijsters, who will battle former world No. 1 Ana Ivanovic in the night match.
The winner of this 13-day event will collect $700,000.