Sharapova’s poor serve proves to be costly with early US Open exit

The 2006 champion, who had been the second favourite for the title, paid for 12 double faults and 60 unforced errors as Pennetta progressed to a fourth-round meeting with Peng Shuai.

The Italian has been ranked as high as 10th and won their last meeting on hard courts in Los Angeles two years ago, so it was by no means a straightforward match for Sharapova.

The Russian survived a stern examination from British teenager Heather Watson in round one after dropping the first set and she made another poor start.

Errors were flowing from the 24-year-old’s racquet in the breezy conditions and she promptly dropped her serve twice in succession. A comeback was inevitable and she put together a run of three straight games, retrieving both breaks, only to drop her serve again, and this time Pennetta capitalised to take the opening set.

Sharapova dug in at the start of the second set to move 3-0 ahead. Four successive breaks of serve kept the third seed just in front and she finally held to level.

Pennetta held serve at the start of the decider and then breaking again when Sharapova sent down an eighth double fault.

The Italian missed two chances for a 4-0 lead, and, although she held for 4-1, it seemed a crucial moment. Sharapova began to take the attack more to her opponent and Pennetta started making more errors, and suddenly they were back all square.

Pennetta held, and Sharapova’s shaky serve faced the ultimate test.

Two double faults were a bad start, a terrific forehand from the Italian set up three match points and, in two hours and 29 minutes, Sharapova was gone, Pennetta smashing a backhand winner to secure a stunning victory.

In the men’s draw, former champion Juan Martin Del Potro eased into the third round with a 6-2 6-1 7-5 victory over fellow Argentinian Diego Junqueira.