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Anja Niedringhaus, Associated Press
Maria Sharapova walks back to her chair, after being defeated by Russia's Alla Kudryavtseva, in their Women's Singles, second round match on the Number One Court at Wimbledon.

WIMBLEDON, England (AP) — Former champion Maria Sharapova was knocked out of Wimbledon in a stunning second-round upset Thursday by a 154th-ranked Russian, marking her earliest exit from a Grand Slam tournament since her first full season on tour in 2003.

Her game littered by double faults and ugly unforced errors, the third-seeded Sharapova slumped to a 6-2, 6-4 loss to 20-year-old Alla Kudryavtseva on Court 1.

"She had nothing to lose," Sharapova said. "She went for her shots. I can't be really happy about anything today."

Sharapova, the 2004 Wimbledon champion at age 17, hadn't lost so early in a Grand Slam since going out in the first round at the Australian and French Open and second round at the U.S. Open in 2003.

Sharapova is the second marquee player eliminated in as many days. But her defeat to a little-known player with a career Grand Slam record of 4-5 was a much bigger shock than No. 3-ranked Novak Djokovic's loss to former No. 1 Marat Safin on Wednesday.

Defending champion Venus Williams, meanwhile, overcame another erratic performance and pulled away to beat Britain's Anne Keothavong 7-5, 6-2 and reach the third round. In men's play, second-seeded Rafael Nadal rallied to beat 19-year-old Latvian star Ernests Gulbis 5-7, 6-2, 6-2, 7-6 (2), 6-3.

On paper, it seemed inconceivable Kudryavtseva could beat the three-time Grand Slam winner and reigning Australian Open champion — especially at the tournament where Sharapova made her major breakthrough four years ago.

Kudryavtseva, who was born in Moscow and now lives in Miami, lost in the first round at Wimbledon to eventual champion Venus Williams last year. She has been ranked as high as No. 59 last year.

In their only previous meeting, Sharapova won easily, 6-1, 6-4, at the French Open last year.

But it was clear from the start Thursday that she was off her game — other than her shrieking grunts, this wasn't the usual Sharapova. She looked listless and finished with 22 unforced errors and eight double faults.

Asked what went wrong, she said, "Not sure. It's a question I'll be asking myself. I think I've got to look at the tape to see what went wrong. It went a little fast to analyze it right now. I felt that I wasn't playing my game. I was letting her take control of the majority of the points."

Sharapova served three double faults in one game and Kudryavtseva took her chances and swept the first set easily in 32 minutes. Kudryavtseva also looked shaky at times in the second set, serving three double faults in the opening game. Sharapova went ahead 2-0, then dropped four straight games.

With Kudryavtseva leading 4-3, Sharapova's second serve on break point was called out, but she challenged the call and the Hawk-Eye replay system showed the ball was in, giving her another chance. When Sharapova served an ace on game point to make it 4-4, she shouted and pumped her fist and seemed to have the momentum.

But Kudryavtseva took the next two games to close out the match. Sharapova double faulted to give her opponent match point, and she converted with a crosscourt forehand winner.

"You can go out there and not feel great and you're opponent can make the most of that," Sharapova said.