Top seed Maria Sharapova [Images] was stretched by Serbia's Ana Ivanovic before she claimed a 7-6, 7-5 win to reach the semi-finals of the Linz Open on Friday.

Fourth-seed Nicole Vaidisova also had to battle hard to overcome another Serb, Jelena Jankovic, 5-7, 7-6, 6-4 and set up a showdown with defending champion Nadia Petrova.

The Russian strolled to a comfortable 6-1 6-3 victory over Australian Samantha Stosur.

In the last of the quarter-finals, third seed Patty Schnyder beat Russian Vera Zvonareva 7-6, 6-4.

Sharapova struggled to overcome an inspired Ivanovic. She failed to serve out either set on her first attempt despite earning early breaks.

"I didn't really finish it off in both sets but credit to her," Sharapova told reporters. "She hung in there and she played a good game in the first set to get back in it.

"In the second set I had two double-faults and made a few sloppy errors but I hung in there."

After breaking Ivanovic in the fifth game of the opening set, Sharapova relinquished the advantage when she produced forehand errors on all three set points at 5-4.

Ivanovic levelled at 5-5 with a glorious forehand winner.

Sharapova then failed to win any of three break points at 5-5 but took the tiebreak 7-3.

The Russian raced to a 5-2 lead in the second set but when she served for the match at 5-3, she dropped her serve with a double fault.

With another tiebreak in prospect, Sharapova broke for the match when Ivanovic ended a lengthy rally by netting a backhand.

FADED AWAY

Stosur performed well against Petrova in the first two games but then simply faded away.

A double-fault gave the second-seeded Russian a break for 2-1, a netted backhand a further break for 4-1, and another double-fault gave Petrova the set.

Petrova dominated the second set by hitting some crisp volleys and rallying strongly from the baseline. She needed just one break of serve to secure victory.

Jankovic mixed up her game with a greater variety of shots but was eventually overpowered by Vaidisova, who fired 20 aces.

The Serbian sixth seed had the edge in the first set as Vaidisova struggled to find her range and hit five double-faults.

Although Vaidisova recovered an early break to level at 3-3, Jankovic regained the advantage to win the set.

After winning the second-set tiebreak 7-5, Vaidisova finally rattled Jankovic in the third game of the decider. A netted backhand from Jankovic gave Vaidisova a 2-1 lead and she kept her focus to win the match.

Mary Pierce's season came to an abrupt end when she was diagnosed as having ruptured a cruciate ligament. The twice Grand Slam champion collapsed on court on Thursday while playing Zvonareva.

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