Venus Williams returns the ball during a third-round match against Marina Erakovic of New Zealand at the Sony Ericsson Open tennis tournament in Key Biscayne, Florida, yesterday. Williams won 6-2, 6-1. - AP

KEY BISCAYNE, Florida (AP):

Justine Henin became the first player to reach the fourth round Sony Ericsson Open yesterday, outlasting a 29-degree (85 Fahrenheit) afternoon to beat Sara Errani 6-2, 6-1.

The heat appeared to be more of a difficulty than Errani, winning 19 of 20 points on her first serve, including five with aces. She was glad to get off the court after only 63 minutes.

"It's very hot out there," she 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."

Joining her later in the fourth round was sixth-seeded Venus Williams, who beat wild-card entry Marina Erakovic 6-2, 6-1.

Henin swept the final three games of the first set and won the final four games of the second set. The Belgian improved to 14-2 this year. 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."

No. 3-seeded Svetlana Kuznetsova had a tougher time. In the second set she had to overcome 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.

"It's lots of pressure because I was not playing any well," said Kuznetsova, the 2004 U.S. Open champion. "I was not awake."

American Ashley Harkleroad lost to Elena Vesnina 6-4, 5-7, 6-4.

No. 13 Dinara Safina rallied past No. 18 Sybille Bammer 4-6, 6-1, 6-0. No. 22 Katarina Srebotnik lost to Caroline Wozniacki 2-6, 6-3, 6-1.

In men's play, No. 9 James Blake outlasted 35-year-old Fabrice Santoro in the afternoon heat, 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, 6-4.0