Isner had 30 aces against Haas, playing in his first tournament since pulling out of Wimbledon because of a torn stomach muscle.

This was Isner's fourth straight win in a third-set tiebreaker. The others were against Tim Henman, No. 8 Benjamin Becker and Wayne Odesnik.

"I have nothing to lose. I can go out and swing away," he said. "I never imagined I would be put in a situation like I've been four times in a row. It's been remarkable."

Isner is 5-2 in tiebreakers this week.

Isner had a match point in the second-set tiebreaker against Haas, but his return was long. He also had a break chance in the third set at 4-all, but his return was wide.

In the final tiebreaker, Isner took a 6-4 lead when a forehand from Haas sailed wide. He closed the match when Haas couldn't handle a serve to his backhand.

"I made one poor mistake in the tiebreak and that cost me the match," Haas said. "He served quite well. I think the tour should come up with a system, where if you're over 6-foot-6 you shouldn't be allowed to play."

Haas never had a break chance against Isner.

Isner will play No. 9 Gael Monfils, who beat third-seeded Marat Safin 6-3, 7-5.

It is the second time this year the Frenchman has reached a semifinal, and the first time this year on hardcourts.

Monfils broke Safin in the second set to take a 6-5 lead, and finished off the match with one of his 14 aces.