KEY BISCAYNE, Fla. — When an infant in the stadium stands began to cry during a rally today, Lindsay Davenport won the point anyway. Motherhood hasn't diminished her focus at work.

Still gaining momentum in her career comeback after becoming a parent, Davenport upset second-ranked Ana Ivanovic 6-4, 6-2 in the third round at the Sony Ericsson Open.

Davenport, 31, left the women's tour in late 2006 to have her first child, then returned last summer. The three-time Grand Slam champion is 17-3 this year, with two titles, and the win over Ivanovic might be her most impressive yet.

The 20-year-old Serb was the Australian Open runner-up, but her game unraveled against Davenport, who broke serve six times and won 13 of 14 points at the net.

Davenport is playing at Key Biscayne for the first time in five years. She next faces No. 13 Dinara Safina, who rallied past No. 18 Sybille Bammer 4-6, 6-1, 6-0.

Top-seeded Justine Henin and No. 6 Venus Williams also reached the fourth round. Henin beat Sara Errani 6-2, 6-1, and Williams defeated wild card Marina Erakovic by the same score.

No. 3 Svetlana Kuznetsova had a tougher time. In the second set she overcame a 5-2 deficit and a match point, and she swept the final 11 games to beat No. 25 Victoria Azarenka 1-6, 7-5 6-0.

No. 22 Katarina Srebotnik lost to Caroline Wozniacki 2-6, 6-3, 6-1. American Ashley Harkleroad was beaten by Elena Vesnina 6-4, 5-7, 6-4.

In men's play, No. 9 James Blake outlasted 35-year-old Fabrice Santoro, 6-3, 6-7 (4), 6-4. No. 16 Paul-Henri Mathieu beat No. 20 Carlos Moya 7-6 (1), 7-5, and Dmitry Tursunov rallied past No. 32 Feliciano Lopez 4-6, 6-3, 6-4.

Henin had more trouble with the sunny, 85-degree weather than with her opponent. The Belgian won 19 of 20 points on her first serve, including five with aces, and she was glad to get off the court after only 63 minutes.

"It's very hot out there," Henin said. "It was quite difficult to breathe. I usually like when it's hot, but I haven't been in this heat for a long time. Even in Australia it wasn't that hot this year, so it's quite difficult."

Henin swept the final three games of the first set and won the final four games of the second set. She's a seven-time Grand Slam champion, but is seeking her first title at Key Biscayne.

Williams is trying for her fourth Key Biscayne title, and her first since 2001. She has lost only 10 games in two matches and was pleased with her latest performance.

"I played consistent and not too many errors, which is great for me," she said. "I was just winning all of the important points."