Top seed Andy Roddick [Images] and number two Tommy Haas moved closer to a showdown at the Legg Mason Tennis Classic with third-round victories on Thursday.

Roddick had some tense moments before defeating Radek Stepanek 6-3, 1-6, 7-5, while Haas booked a spot in the quarter-finals with an easy 6-3, 6-4 triumph over American Michael Russell.

Stepanek won in Los Angeles two weeks ago and gave Roddick all he could handle on a cool night in Washington. The Czech blasted 20 aces and lost his serve only twice.

"He's been playing well," Roddick said. "You don't win the first tournament of the US Open series by accident.

"It was probably the toughest draw for both of us as far as potential players you could play in that round."

Roddick had 12 aces in the opening set and appeared ready to roll over the 63rd-ranked Stepanek. But the 15th seed played an inspired second set to force a final frame.

At 4-4 in the third set, Stepanek had a double-break point on Roddick's serve but the American survived and ultimately closed out the match on a service break at 30.

"The second set he got away with poking it in and I was being overly aggressive and making the error," said Roddick, who had 23 aces in the match.

"So I tried to draw back a little bit in the third set, especially on the big points, and make him try to create something."

In the quarter-finals, Roddick will play South Korean Hyung-taik Lee, while Haas will face the 6 ft 9 ins American upstart John Isner.

Haas showed no lingering effects from his Wimbledon injury, when he withdrew prior to his fourth-round match against Swiss world number one Roger Federer [Images] with a torn stomach muscle.

Playing in his first tournament since the injury, the 12th-ranked Haas needed just one hour, 11 minutes to subdue 29-year-old Russell in their first career meeting.

The German broke Russell's serve in the second game of the opening set and in the third game of the final set and made them hold up.

"It always helps getting that early break in each set," he said. "You just have to hold your serve after that to confirm your break. It also gives me a little time to relax."

Haas landed only 45 percent of his first serves but blasted 10 aces to keep the 71st-ranked Russell off balance for much of the match.

Isner, who lost in the 2007 NCAA singles finals while at the University of Georgia, beat qualifier Wayne Odesnik 6-7, 7-6, 7-6, the third consecutive match he has won in a third-set tiebreaker.

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