Top seed Maria Sharapova [Images] controlled her powerful but erratic groundstrokes in the decisive third set to thwart an upset bid by fellow-Russian Nadia Petrova on Tuesday to reach the semifinals at the U.S. Open.

"It's absolutely amazing. I can't believe I pulled this match out today," Sharapova said after the 7-5, 4-6, 6-4 victory.

"There were a lot of ups and downs. There were times when I felt like couldn't make anything."

Sharapova made 48 unforced errors, including 40 in the first two sets, while Petrova committed 50 in the two-hour, 30-minute struggle.

Sharapova, who lost only 12 games in her first four victories, battled the ninth seed evenly over the first two sets of fierce hitting but questionable accuracy, before harnessing her power in the third set of the quarter-final.

Finding the range on her powerful forehand, Sharapova began cracking winners and broke Petrova in the second game on her way to a 3-0 lead.

Petrova, who has yet to win a WTA Tour singles title, battled back from 2-5 down in the third set and held two game points on her serve from 40-15 to level the set at 5-5.

Sharapova, however, forced deuce and claimed victory when Petrova's backhand drive drifted wide.

The 23-year-old Petrova nearly ousted the tournament's top seed for a second year in a row. Last year she eliminated top seed Justine Henin-Hardenne of Belgium 6-3, 6-2 in the fourth round to reach the quarters.

Sharapova, who made it only to the third round at the 2004 Open, also reached the semifinals this year at the Australian Open and at Wimbledon, where she beat Petrova 7-6, 6-3 in the quarter-finals.

The 18-year-old Sharapova will next play either fourth seed Kim Clijsters [Images] of Belgium or 10th seed former Open champion Venus Williams [Images] of the United States.

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