MELBOURNE, Australia - Andy Roddick's aces had the crowd buzzing as he rode his big serve into the fourth round of the Australian Open.

Hitting the ball better as the match went on, Roddick dropped only seven points in his last 10 service games today and finished with 22 aces to beat Austrian Jurgen Melzer 6-2, 6-2, 7-5. Roddick also made one of the shots of the day - a between-the-legs winner with his back to the net while chasing down a lob.

After beating three consecutive left-handers, next up for Roddick is 102nd-ranked Philipp Kohlschreiber, a German with a 10-18 career record who won only one Grand Slam match before this tournament.

On a warm, sunny day perfect for dozing, Roddick quickly woke up the crowd, starting his first service game with a pair of aces. He soon was cracking serves at up to 139 mph. Melzer, seeded 32nd, had three break points in Roddick's next service game, then never got another chance.

"I thought I moved really well. I got up two sets, the third one got a little tight, but I was able to get through," said Roddick, noting his serve isn't yet nearing his world record of 155 mph. "I'm holding serve though, that's the most important thing."

Seventh-seeded Tim Henman of Britain pulled off his own stunner, a reflex volley behind his back into an open court. But it was the only highlight for Henman, who reached at least the quarterfinals in the last three Grand Slams. He committed 32 unforced errors and five double-faults in falling to 26th-seeded Nicolay Davydenko 6-4, 6-2, 6-2.

Australia's Lleyton Hewitt, cheered on by boisterous home fans in a night match, overcame No. 25 Juan Ignacio Chela 6-2, 4-6, 6-1, 6-4. The third-seeded Hewitt broke Chela seven times and had 39 winners. He closed out the match with his ninth ace, but clearly wasn't happy with his 37 unforced errors.

Asked to rate his performance on a scale of 1 to 10, he said "about a 2."

"I felt like I played O.K. tonight," Hewitt said. "As they say, you can't win a Grand Slam in the first week, but you can lose it."

He next faces Spain's Rafael Nadal, who had been touted as a rising star before an ankle stress fracture sidelined him for three months last year. He ousted American qualifier Bobby Reynolds, who has practiced with Roddick in Australia, 6-1, 6-1, 6-3.

French Open finalist Guillermo Coria beat former No. 1 Juan Carlos Ferrero 6-3, 6-2, 6-1.

Women's French Open champion Anastasia Myskina joined Russia's two other Grand Slam title holders in the fourth round when American Lisa Raymond withdrew with a torn abdominal muscle that forced her to retire from her doubles match Friday after one game.

"I'm extremely disappointed because I couldn't have asked to play better in my first two matches," said Raymond, who hopes to return for the Indian Wells tournament in California starting March 9.

Top-ranked Lindsay Davenport beat 15-year-old Czech qualifier Nicole Vaidisova 6-2, 6-4 to move into a fourth-round match against 13th-seeded Karolina Sprem, who ousted Russia's Elena Likhovtseva 6-4, 6-3.

Sixth-seeded Elena Dementieva became the seventh Russian woman to advance when she outlasted Daniela Hantuchova 7-5, 5-7, 6-4. Hantuchova committed 78 unforced errors and bloodied her knee in a fall in the second set. Dementieva next meets No. 12 Patty Schnyder of Switzerland, a 7-6 (4), 6-3 winner over American Amanda Spears.

No. 8 Venus Williams overcame early errors to win the last nine games in a 1-hour, 6-3, 6-0 rout of Anna Smashnova.

After holding at 3-3, Smashnova never had more than two points on her serve as Williams took advantage of her looping, heavy topspin groundstrokes.

"She just played a different-pace game, so I pressed a little too much and was hitting the balls a bit long," Williams said. "I needed to add some spin because she's the kind of player where you don't want to get caught up playing her game. That's when things can really get kind of strange. So I kept with my game, playing aggressive, and worked through the errors."

Tenth-seeded Alicia Molik closed a 6-3, 6-2 win over Tatiana Panova with an ace, advancing to face Williams.

"Bring it on!" Molik told the crowd at Rod Laver Arena after reaching the fourth round, matching her best run at a major.