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 today.

Errors were flowing from the 24-year-old’s racquet in the breezy conditions and she promptly dropped her serve twice in succession to trail 4-0.

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 was still making far too many errors but she 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 the match.

Pennetta reached the quarter-finals in 2008 and 2009 and she was not about to lie down, holding 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.

The Russian piled the pressure on her opponent but Pennetta held, and suddenly Sharapova’s shaky serve was facing 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.