Champion Maria Sharapova [Images] did just enough to keep her Wimbledon [Images] defence alive on Saturday with a scrappy 6-2, 6-4 win over Slovenia's Katarina Srebotnik.

While there was more base metal than gold in her performance on Court One, the Russian will be happy to have got the first week out of the way at the All England [Images] Club.

Second seed Sharapova was joined in the fourth round by a resurgent Mary Pierce.

The 30-year-old Frenchwoman, a first round loser last year, blasted Serbian teenager Ana Ivanovic 6-1, 6-4.

It has been nine years since Pierce last reached the quarter-finals at Wimbledon and she has never looked so at ease on grass.

Runner-up at the French Open earlier this month, the 12th seed is enjoying her tennis again and the slick lawns are aiding her power game this year.

Eighth seed Nadia Petrova also advanced with ease, the Russian beating Zimbabwe's Cara Black 6-4, 6-3.

MARTINEZ FALLS

Former champion Conchita Martinez fell, however, a 6-4, 6-1 victim of Czech Kveta Peschke.

The oldest woman left in the draw and contesting her 63rd Grand Slam tournament, 33-year-old Martinez flopped on an overcast court 18.

Peschke, who had lost both the pair's previous matches, faces Petrova next.

Sisters Venus and Serena Williams [Images] -- with two Wimbledon titles each -- are in action later on Saturday.

Venus tackles Daniela Hantuchova [Images] and Serena plays fellow American Jill Craybas.

Fellow former world number one Kim Clijsters [Images] is also on court, against Italy's [Images] Roberta Vinci.

Men's second seed Andy Roddick [Images], who finished his rain-delayed second round match on Friday, faces Russia's [Images] Igor Andreev while Britain's last remaining hope, Scotland's Andy Murray, clashes with former runner-up David Nalbandian.

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