The defending champions - Roger Federer of Switzerland and Maria Sharapova of Russia - have advanced to the fourth round of the Wimbledon tennis championships in London.

Federer, the top seed, scored a four-set win over Nicolas Kiefer of Germany Saturday, 6-2, 6-7, 6-1, 7-5. The two-time defending champion next faces 2003 French Open winner Juan Carlos Ferrero of Spain, who scored a four-set win over Florian Mayer of Germany (3-6, 6-2, 6-1, 6-1).

Sharapova, the second seed, reached the round of 16 for the third time in her career, 6-2, 6-4. Sharapova will play France's Nathalie Dechy, a straight-set winner over Alyona Bondarenko of Ukraine (6-1, 6-4).

Elsewhere in the ladies' draw, world number one Lindsay Davenport of the United States scored a straight-set win over Dinara Safina of Russia (6-2, 6-1). Davenport takes on Belgium's Kim Clijsters, who ousted Roberta Vinci of Italy (6-3, 6-4).

Eighth-seeded Nadia Petrova became the sixth Russian woman in the round of 16 when she defeated Zimbabwe's Cara Black in straight sets (6-4, 6-3). Petrova takes on Kveta Peschke of the Czech Republic, who knocked 1994 champion Conchita Martinez of Spain out of the grass-court tournament (6-4, 6-1).

French Open runner-up Mary Pierce defeated Ana Ivanovic of Serbia and Montenegro (6-4, 6-1). Pierce will play Flavia Pennetta of Italy, who ousted Eleni Daniilidou of Greece (6-4, 6-3). Two-time champion Venus Williams of the United States ousted Daniela Hantuchova of Slovakia in straight sets, 7-5, 6-3. Venus will play either her younger sister Serena Williams or American countrywoman Jill Craybas.

In men's play, last year's runner-up Andy Roddick of the United States scored a straight-set win over Igor Andreev of Russia (6-2, 6-2, 7-6). Roddick plays the winner of a match between Guillermo Coria of Argentina and Jurgen Melzer of Austria.

Max Mirnyi of Belarus scored a four-set win over Jiri Novak of the Czech Republic (5-7, 7-5, 6-4, 7-6). Mirnyi next plays Sweden's Thomas Johansson, a straight-set winner over Serbia and Montenegro's Janko Tipsarevic (6-2, 6-3, 6-1).

Dmitry Tursunov of Russia, who ousted Britain's Tim Henman earlier this week, defeated German Alexander Popp (5-7, 7-6, 6-2, 6-2). The Russian faces ninth-seeded Sebastien Grosjean of France, a four-set winner over Serbia and Montenegro's Novak Djokovic (7-5, 6-4, 5-7, 6-4).

Russian Mikhail Youzhny celebrated his 23rd birthday with a four-set win over Jonas Bjorkman of Sweden (7-5, 6-3, 3-6, 7-6). Youzhny takes on Fernando Gonzalez of Chile in the fourth round.

Some information for this report provided by AP.