MELBOURNE (AP) ― Maria Sharapova advanced to the third round of the Australian Open without losing a game, and No. 4 Agnieszka Radwanksa extended the best winning streak of the year to 11 matches on Wednesday.

But Sam Stosur wilted again under the pressure of expectations at home, the 2011 U.S. Open champion twice failing to serve out the match before losing 6-4, 1-6, 7-5 to China’s Zheng Jie in a second-round upset.

No. 2-ranked Sharapova, the runner-up here last year, had a 6-0, 6-0 win over Misaki Doi in 47 minutes, conceding just 15 points to the Japanese player. The reigning French Open champion hasn’t seemed to be troubled at all by a right collarbone injury that ruled her out of a warmup tournament in Brisbane. Sharapova beat fellow Russian Olga Puchkova 6-0, 6-0 in the first round, and has so far only spent 1 hour, 42 minutes on court in two matches at Melbourne Park.

No. 9 Stosur couldn’t close out her opponent. She was leading 5-2 in the third set and was only two points from advancing to the third round before Zheng, the first Chinese player to reach a Grand Slam semifinal when she made the last four at Wimbledon in 2008, reeled off five straight games to end Australia’s involvement in the women’s draw.

It extended a miserable run at home for Stosur, who lost in the first round here last year in her first major after beating Serena Williams in the U.S. Open final. Her first-round win on Monday was her first in five matches at home.

Radwanska had earlier rolled into the third round with a 6-3, 6-3 victory over Romania’s Irina-Camelia Begu and remains unbeaten this year, including titles at warmup tournaments this month at Auckland and Sydney.

“I can play even better,” said Radwanska.