World No. 1 Justine Henin and defending champion Serena Williams both had an easy day and advanced into the top 16 of the Australian Open women's single event with straight sets wins in Melbourne yesterday.

Henin had serving troubles in the match but she overcame it to hold off Francesca Schiavone 7-5, 6-4 in the third round.

Henin had only 48 percent of her first serves but was lucky enough to win the game.

"It was really exciting. I'm glad to win in two," Henin said. "She's always given me trouble in the past, so it was a tough third round for me."

Defending champion Serena Williams trounced Victoria Azarenka 6-3, 6-4, improving her record to 26-1 at Melbourne Park since the start of 2003.

Williams, who was unseeded and ranked No. 81 when she beat then top-seeded Sharapova here last year to claim her eighth grand slam title, fired 15 aces to dominated the match.

"I feel pretty good about where I am," she said. "Hopefully I'll peak later in the tournament." said Williams.

Fifth seed Sharapova also eased past fellow Russian Elena Vesnina 6-3 6-0 while third seed Jelena Jankovic had a 6-2, 4-6, 6-1 win over Virginie Razzano of France.

In men's single, second seed Rafael Nadal overcame a slow startto finish a 7-5, 6-2, 6-3 win over French Gilles Simon in two hours 25 minutes.

Fourth seed Nikolay Davydenko defeated another Frenchman Marc Gicquel 6-3, 6-2, 6-3 to book another fourth round place.

The world number four Davydenko finished top eight or better in six of his last Grand Slams, but he had never enter the semifinal of the Australian Open.