US Open 2011: Flavia Pennetta beats Maria Sharapova

Sharapova came into the tournament on the back of winning in Cincinnati

Italy's Flavia Pennetta sent third seed and former champion Maria Sharapova tumbling out of the US Open with a shock third-round win.

Pennetta, the 26th seed, came through 6-3 3-6 6-4 in a dramatic match on Arthur Ashe Stadium.

Sharapova had been among the favourites for the title after winning the build-up tournament in Cincinnati last month.

Second seed Vera Zvonareva beat Anabel Medina Garrigues, conqueror of Britain's Laura Robson, 6-4 7-5.

And ninth seed Sam Stosur won a dramatic match against 24th seed Nadia Petrova that lasted three hours and 16 minutes, with the Australian failing to serve it out in the second set but eventually prevailing 7-6 (7-5) 6-7 (5-7) 7-5.

Sharapova struggled with her game against Pennetta, making 12 double faults and 60 unforced errors in an erratic performance.

The Russian lost the first four games of the match but battled back to take the second set, and again from a break down in the decider.

But when she had to serve to stay in it at 5-4 down, Sharapova opened with two double faults before Pennetta clinched victory with a thumping backhand winner.

"I made way too many unforced errors," said Sharapova.

"I fought back to get myself back in the match in the third set. I think the first three, four games, on every game I had a chance to win that game, whether it was a break point or it was a game point on my serve, and I didn't win those games.

"When you're down 1-4 and you get yourself back in a position where you can win again and then start making errors, it's just too inconsistent to win the match against her."

Pennetta said: "It was a great win for me," said Pennetta. "I think in the third set I was a little bit nervous when I started to think too much about closing the match, so I'm really proud of my game today."

Romania's Monica Niculescu thrashed Czech 27th seed Lucie Safarova 6-0 6-1 to set up a surprise last-16 match against Germany's Angelique Kerber, who beat Alla Kudryavtseva 6-3 6-1.

Germany's Sabine Lisicki, the 22nd seed and Wimbledon semi-finalist, defeated American Irina Falconi 6-0 6-1, while 13th seed Peng Shuai of China beat German 19th seed Julia Goerges 6-4 7-6 (7-1).

In the night session, Russian 25th seed Maria Kirilenko ended the run of American hope Christina McHale 6-2 6-3.