Sydney, Mar 31: Former world number one Lindsay Davenport beat Serbian second seed Ana Ivanovic 6-4 6-2 to reach the fourth round of the Sony Ericsson Open.

The American's win denied Ivanovic a chance to seal back-to-back titles after her victory at Indian Wells.

Seeds Ana Chakvetazde and Daniela Hantichova lost, Svetlana Kuznetsova saved a match point before winning and Serena Williams won in three sets.

Rafael Nadal beat Nicolas Kiefer 6-2 6-4 to reach the men's fourth round.

The world number two's match was interrupted by rain but the Spaniard still managed to complete his second straight match without facing a break point.

"It was not the best day because I was playing unbelievable in the beginning, hitting very well the ball, and playing an almost perfect match," he said.

"When I come back to the court the ball was a little bigger and slower, and it was a little bit more difficult for me.

Next up for Nadal is France's Paul-Henri Mathieu, who ousted Carlos Moya of Spain 7-6 (7-1) 7-5.

Ivanovic appeared to have no answer against the aggressive game of Davenport, who is now world number 33.

The Serbian is the second top 10 player Davenport has beaten since returning to the tour last September after giving birth to her first child last June.

Davenport won 13 of 14 points at the net and led 6-4 3-0 when it appeared Ivanovic might fight back when she broke serve in the fourth game.

However, the American broke straight back in the next game and cruised to victory.

Fifth seed Chakvetazde of Russia was beaten 7-5 6-1 by Germany's Sabine Lisicki, while seventh seed Hantuchova of Slovakia slipped to a 6-4 6-7 (8-10) 7-5 loss to Japan's Ai Sugiyama.

Kuznetsova, the 2004 US Open champion, trailed 5-2 before winning the final 11 games of the match to beat Bulgaria's Victoria Azarenka 1-6 7-5 6-0.

Serena Williams lost the first set to Italy's Flavia Pennetta but fought back to win 6-7 (6-8) 6-3 6-2.

Top seed Justine Henin, fourth seed Jelena Jankovic and sixth seed Venus Williams had no problems advancing to the fourth round.

Henin, in her first tournament after a month off, beat Italian Sara Errani 6-2 6-1 while Venus defeated New Zealand's Marina Erakovic by the same score.

Other results in the men's competition saw US ninth seed James Blake oust France's Fabrice Santoro 6-3 6-7 (4/7) 6-4 and Czech 10th seed Thomas Berdych beat Spain's Juan Carlos Ferrero 6-1 6-3.