Maria steamrolls Mary

Pierce started the match well, holding her own during the opening skirmishes in the first set until Sharapova began to exert her class, pushing her opponent to the limit to take the first set with relative ease.

The French player, evidently lacking a degree of fitness, had no answer to the Russian's precision hitting, and the more she was stretched around the court, the more Sharapova looked in complete control, as she went on a storming run of seven consecutive won games.

In the fifth game of the second set, Pierce showed signs of a recovery, serving well to pull back to within one of the Russian at 2-3. But from that moment on, it was all Sharapova, and she steamrollered last year's San Diego winner to book a date with Patty Schnyder in the last four.

The Swiss player had earlier advanced to the semi-finals with a 6-4 6-3 win over Elena Dementieva of Russia.

It was not a classic Schnyder performance but the number five seed did enough to capitalise on her opponent's errors to book a place in the last four.

Indeed, Dementieva's unpredictable play was more responsible for Schnyder's victory than anything the Swiss player could produce.

The Russian produced some moments of brilliance, most notably with some powerful serves, but all too often she misfired with her forehand, and Schnyder was there to take advantage.

Schnyder's game was steady if unspectacular and she rarely showed glimpses of her early summer form, but progress she did and now she faces a real test against Sharapova if she is to reach the final.

Earlier, 17-year-old Nicole Vaidisova became the first player into the semi-finals with a three set 3-6 6-4 6-3 win over Anna Chakvetadze of Russia.

The Czech teenager will now meet either Martina Hingis or Kim Clijsters - who play in the last of the day's quarter-finals - in the last four.