Former Wimbledon champion Sharapova won in Tokyo last week
Local hero Peng Shuai produced another shock at the China Open by beating Russian Maria Sharapova 6-2 6-4 to advance to the quarter-finals.
Sharapova, who claimed her first title since returning from a shoulder injury in Tokyo last week, looked tired having played a three-hour match on Tuesday.
She was broken twice in the first set and in the sixth game of the second.
Sharapova saved two match points in the final game before finding the net with a forehand to hand Peng victory.
"I was having trouble with a few things," said Sharapova. "It was not my day I guess.
"Usually I'm able to fight and get myself going when things are not going well and I was not able to do that today for some reason.
"I'm not sure why, but sometimes you have those days."
Peng, world number 53, who beat defending champion Jelena Jankovic in the second round, now faces either Serena Williams or Nadia Petrova.
Svetlana Kuznetsova, the 2006 champion, booked her place in the last eight with a 6-3 4-6 6-0 victory over Ukraine's Alona Bondarenko.
She now faces fellow Russian Anastasia Pavlyuchenkova who defeated Aleksandra Wozniak of Canada 6-4 6-4.
Dinara Safina, deposed by Serena Williams as world number one this week, and Venus Williams have already bowed out of the tournament.