Roddick lost the last five games of the second set, his serve broken twice, and struggled through the third, rescuing a break point in the fifth game and two in the ninth, the second when Stepanek sent a backhand wide.

"I just kind of hung around," Roddick said. "I decided to put the ball in the court and if he was going to be aggressive and get it, too good. I tried to draw back in the third set, make him create something."

Stepanek, who fired 20 aces, was two points from forcing a tiebreaker in the final game but sent a forehand long to hand Roddick a match point and netted a forehand to fall after one hour and 50 minutes.

"He served pretty well," Roddick said. "He got through his service games without me getting to him. You just hang around long enough and something else might happen."

German second seed Haas continued his comeback, defeating American Michael Russell 6-3, 6-4. He withdrew from Wimbledon a month ago with a torn stomach muscle before a round of 16 match against Swiss world number one Roger Federer.

Next for Haas is 22-year-old US novice John Isner, who played only one ATP match before Monday. The tall Cinderella man fired 31 aces to defeat countryman Wayne Odesnik 6-7 (4/7), 7-6 (7/3), 7-6 (7/2).

Russian third seed Safin reached his fourth quarterfinal of the year, all on hardcourts, by ousting 104th-ranked Dutchman Robin Haase 7-5, 6-7 (2/7), 7-5 after two hours and 35 minutes in a match that ended 47 minutes after midnight.

Safin faces Frenchman Gael Monfils on Friday. Confident Monfils, ranked 54th, beat Germany's Michael Berrer 6-7 (5/7), 6-3, 6-3.

"Quarter-final for me is nothing. I expect to win this tournament," said Monfils, whose only ATP title came on Sopot clay in 2005. "(Safin is) nothing. I played him last year in Cincinnati and I beat him. It's just a match."

World number five Roddick, who won here in 2001 and 2005, advanced to his 10th quarterfinal of the year. On Friday he faces South Korean fifth seed Lee, who rallied to eliminate France's Julien Benneteau 2-6, 6-2, 6-3.

"He times his winners," Roddick said of Lee. "You've got to try to make him uncomfortable, break his rhythm a little because he's a rhythm player."

Roddick, who lost an Indianapolis semi-final last week, seeks his second title of the year after winning at Queen's in June. He improved to 3-0 lifetime over Stepanek, who won his second ATP title two weeks ago in Los Angeles.

Haas, who only resumed full workouts Monday, was pleased with his progress.

"So far, so good," said Haas. "To reach quarter-finals is good, especially with the injury. I'm happy so far."

Isner, who in May led the University of Georgia to a US college team title, ousted Britain's Tim Henman and German eighth seed Benjamin Becker in earlier third-set tiebreakers at the 600,000-dollar US Open tune up event.

"It's still a dream. To win three matches 7-6 in the third at a tournament like this is amazing," Isner said. "I know my serve can take me a long way. Hopefully it can carry me against Haas. He's a great player."

Ninth-ranked Haas, one victory shy of 400 in his ATP career, seeks his 12th title and second of 2007, having won February's Memphis final over Roddick. Isner, who is 6-foot-9, has yet to win a first set in four career ATP matches.

"I know he serves really big," Haas said of the newcomer. "I don't know the last time somebody won three in a row 7-6 in the third. It's tough to play those players. He uses his height as an advantage. You have to respect it."

Even Roddick respects it.

"You can't teach 6-foot-9," Roddick said. "He's playing on the house's money. If you have that kind of weapon you're going to win matches out here."