KEY BISCAYNE, Fla. — Justine Henin leaned on the net as if she had completed a strenuous workout, even though she won easily today at the Sony Ericsson Open.

Sunny, 85-degree weather gave the top-ranked Henin more trouble than her opponent, and she became the first player to reach the fourth round by beating Sara Errani 6-2, 6-1. Joining her later in the fourth round was sixth-seeded Venus Williams.

Henin won 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."

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.

No. 3-seeded Svetlana Kuznetsova had an even 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.

Williams defeated wild-card entry Marina Erakovic 6-2, 6-1. Dmitry Tursunov became the first man to reach the fourth round by rallying past No. 32 Feliciano Lopez 4-6, 6-3, 6-4.