Second seed Andy Roddick [Images] saw plenty of room for improvement after he eased into the quarter-finals of the Australian Open with a 6-3, 7-6, 6-1 win over lowly-ranked Philipp Kohlschreiber of Germany [Images] on Monday.

The big-hitting American was never in any serious trouble against Kohlschreiber, at 102 the lowest-ranked player left in the tournament, but later said it was probably his least convincing performance of the tournament.

Fortunately for Roddick, the 2003 U.S. Open champion and last year's Wimbledon runner-up, even an off day can still mean a fairly comfortable win.

"I just felt like I was fighting it a little bit more than I had in the first three rounds," Roddick said.

"The good thing is I don't feel like I had my best day and we're sitting here talking about a three-set win," he said.

Roddick will play either 12th seed Guillermo Canas of Argentina or 26th seed Nikolay Davydenko in a bid to match his 2003 semi-final appearance.

"I think it's going to be probably a similar match either way. They're both going to make me work very hard," he said.

"They're both really good returners so it will be a little bit of a different match than I've played so far," Roddick said.

POWERFUL SERVES

Kohlschreiber was playing in only his third Grand Slam after two early exits at the U.S. Open but was able to match Roddick's powerful serve in the first two sets.

He slammed three of his five aces in the second set on his way to forcing the tie-breaker, which the American won 8-6.

Roddick stamped his authority on the match in the final set when he broke the 21-year-old German's serve in the second and fourth games before serving out the match after 87 minutes.

Roddick said he had struggled to find his range early in the match on Vodafone Arena at Melbourne Park but was happy he had been able to win the important points.

He put part of the trouble down to getting used to playing a right-handed opponent again after seeing off two left-handers in his previous two matches.

Roddick beat unseeded Briton Greg Rusedski [Images] in four sets in the second round and then had a straight-sets win over 32nd seed Jurgen Melzer of Austria in the third round.

"I didn't hit the ball as clean as I did in the first three matches," Roddick said.

"I think I actually had a little trouble getting used to a serve coming from a righty in the first couple of sets, as weird as that sounds," he said.

Roddick admitted that while he was able to hit 15 aces past the German, he had been most pleased with getting a consistently high percentage of first serves into play.

"The last three matches I think I've been putting the first serves in play a lot and that has been helping me out," he said.

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