MELBOURNE, Australia -- U.S. Open champion Serena Williams turned from survivor to aggressor Saturday, slugging her way into the fourth round of the Australian Open with a 6-2, 7-6 (2) victory over Sabine Appelmans.

Williams floundered through her first match and much of her second, but was dictating points from the start against Appelmans.

	Martina Hingis has yet to lose a set at this year's Australian Open.

Williams, 18, yielded only three points on serve in her first set. Appelmans picked up her game in the second, when Williams had to save break points in the third and ninth games.

She erased the first with a pair of excellent retrievals that pushed Appelmans into hitting a forehand wide. She took care of the second by slamming a forehand down the line, punctuating it with a loud "Yeah!"

In the tiebreaker, the third-seeded Williams jumped to a 3-0 lead, catching her Belgian opponent flatfooted with a cross-court forehand and then drawing two errors. She reached 4-1 with an ace and 6-1 with a cross-court backhand, ending the 71-minute match when Appelmans hit a backhand serve return into the net.

"I played better and I was more mentally stable than I was in my other matches. I still, however, feel I'm a little rusty and there is so much more improvement I can do," said Williams, who had not played a match since October before starting the tournament here Tuesday.

She said that reaching No. 1 is her goal "now more than ever."

Appelmans noted Williams' patchy opening rounds, but said, "I think she will improve. She has the ability to go all the way if she's fit."

Appelmans said she was expecting harder, flatter shots from Williams.

"She hits her forehand with a lot of topspin. ... It was very hard but it's different to the other girls. It's more like how the men play," said the 27-year-old Belgian, a quarterfinalist here in 1997.

Adding to the problem, she added, "I had a lot of trouble with her second serve, her kick serve."

Williams, who served at up to 115 mph, will play No. 16 Elena Likhovtseva, a 5-7, 7-6 (5), 6-3 winner over Belgian Els Callens.

Williams' match was the second on center court interrupted by rain and then resumed after the roof was closed.

The same thing had happened earlier in the day to Martina Hingis.

Now entering "middle age," Hingis is happy with the way she is beating younger women at the Australian.

In three matches, the three-time defending champion has lost only 14 games.

Against 18-year-old Australian Alicia Molik, Hingis faced serves of up to 116 mph, and returned some of the hardest, in a 6-2, 6-3 victory that took her into the fourth round. Hingis' second serve is tougher than ever, Molik said, but she didn't need it much, putting in 74 percent of her first serves.

Hingis said she has had to concentrate hard because her first three opponents "were all younger than me, youngsters coming up, having nothing to lose."

She beat Croatia's Mirjana Lucic and Belgium's Justine Henin before Molik.

"Three in a row," she said of the rarity of a 19-year-old playing that many younger opponents back-to-back. "I feel a little bit like on the tour that I'm getting to that middle age, 20s, slowing."

But, she said, getting better. She agreed with Molik's assessment of her second serve, and said, "My game all around has got a bit better."

She also is hungrier to win, she said, "because now I know what the whole thing is all about."

"What better situation can you get?" Hingis asked. "Everything's just show business. You see the papers, you are in the pictures, and it's so much fun, traveling and meeting people."

Molik, the fastest woman server so far in this tournament, had six aces and a few spectacular points, including one she launched with a 116 mph serve and followed up with a deep solid volley and a drop volley.

But once a rally started, the Australian had no answer for Hingis' deep groundstrokes and frequent net attacks.

"If I saw anything short, any weak or second serve, I was going to attack that," Molik said. "I wasn't able to do that."

The first rain delay, 46 minutes on the retractable-roof center court, extended to four hours on outside courts.

In a match moved into the main stadium, No. 6 Barbara Schett beat Argentine qualifier Florencia Labat 6-1, 6-3. She next plays No. 13 Arantxa Sanchez-Vicario, a 7-5, 6-1 winner over Australian wild-card entry Bryanne Stewart.

American Kristina Brandi advanced to a meeting with No. 10 Conchita Martinez by beating Romania's Ruxandra Dragomir 6-4, 7-6 (7). Martinez defeated Croatia's Jelena Kostanic 6-4, 6-4.