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Maria Sharapova overcame the sternest test yet of her defending champion credentials before booking her place back in the Wimbledon semi-finals.

The 18-year-old second seed was stretched to the limit by her gutsy Russian compatriot Nadia Petrova before fashioning a nervy 7-6 6-3 victory.

Sharapova edged through the first set tie-break 8-6 and also had to rely on a lucky net cord at break point down when serving for the match to stay on track.

While Sharapova could consider herself highly fortunate to maintain her proud record of not losing a set in this year's competition, she also displayed the courage and tenacity to suggest she remains favourite to retain her crown.

Amelie Mauresmo secured her place in the semi-finals for the second successive year with a straight-sets win over Anastasia Myskina on Centre Court.

The number three seed needed just over an hour to secure a 6-3 6-4 victory.

Mauresmo, who had lost just 15 games in her four matches before today, again used her serve-and-volley game to great effect, which left the 2004 French Open champion with few opportunities to break her rhythm.

Mauresmo will now meet Lindsay Davenport in the semis.

The top seed remained on course for her second Wimbledon title with a hard-fought quarter-final victory over Svetlana Kuznetsova.

Davenport was twice a break up against the US Open champion in the opening set but needed a tie-break to finally win it on court one.

The 1999 champion then raced into a 3-0 lead in the second set but was made to fight all the way before securing a 7-6 6-3 victory with her eighth ace of the match.

Finally Venus Williams served warning that Grand Slam success is back on the family agenda when she powered into the semi-finals with a Centre Court defeat of Mary Pierce.

The former world number one demonstrated the type of form which brought her back-to-back Wimbledon singles titles in 2000 and 2001, defeating Pierce 6-0 7-6 in one hour and 29 minutes.

Williams is noted for her erratic shot-making, but on Tuesday her game could not have been more precise as she took this year's French runner-up apart in the first set.

It was always going to be a struggle for Pierce after she gifted her first service game to Williams with a rash double fault.