NEW YORK -- It had all been so easy for Andre Agassi, embarked on a straight-sets march through the U.S. Open, rarely challenged in his first four matches.

	Andre Agassi dropped his first set of the U.S. Open, but rebounded to beat Max Mirnyi in four sets.

And then came Max Mirnyi.

Agassi, seeded No. 6, had his hands full with the No. 32 seed for a while Wednesday night before coming from behind to advance to the semifinals 6-7 (5), 6-3, 7-5, 6-3.

''I thought it was a high-standard match from start to finish,'' Agassi said. ''The first set I let slip away. I had a couple of opportunities. In the end, he raised his game and won the right points. In the second set, he donated a few opportunities back to me.

''You don't think about losing or winning a set up or a set down. You think about 'What do I need to do here to get my teeth deeper into this match?' ''

And that's when he bit into it, raising his game, taking advantage of almost every opportunity.

Next up for Agassi is defending champion Lleyton Hewitt, the No. 1 player in the world. Hewitt advanced with a 6-1, 7-6 (6), 4-6, 6-2 victory over Younes El Aynaoui.

The other semi will be set on Thursday, when No. 11 Andy Roddick meets four-time Open champion Pete Sampras, seeded No. 17, and No. 26 Fernando Gonzalez plays No. 24 Sjeng Schalken, in the quarterfinals.

The 6-foot-5 Mirnyi drilled 19 aces at Agassi, dodged 11 of 17 break points, won the first-set tiebreaker, and still lost the match.

''He's a big guy who hits the ball big off both sides,'' Agassi said. ''He can use his size to force you to do something special on any given point. He served big. He volleyed soundly. I had to play well tonight.''

Agassi, a two-time winner of this event, simply imposed his will on Mirnyi, who was playing in his first Grand Slam quarterfinal.

The turning point came in the third set. After they split the first two sets, Mirnyi was serving at 4-4 in the third. On his first serve, he was distracted by a fan's scream as he hit the ball.

Agassi refused the fault, allowing Mirnyi another first serve, and then won the point. Mirnyi, distracted for the moment, battled back, forcing the game to deuce seven times before winning it on a 124-mph serve, his 15th ace of the match.

After Agassi held his serve, Mirnyi double-faulted on the first point of his serve, fell into a triple-break hole and surrendered the edge. Agassi then served out the set and rolled through the fourth set to secure the match.

At 32, Agassi is attempting to become the oldest player to win this event since Ken Rosewall captured it at age 35 in 1970.

Hewitt advanced earlier in the day, wearing down El Aynaoui, who had played his previous match until 2:15 in the morning because of a rain delay. Hewitt won the first set easily, took the second-set tiebreak and then, after losing the third, secured the match as El Aynaoui seemed to run out of energy.

The defending champion views Agassi as a difficult challenge.

''It's going to be a tough match,'' he said. ''I've got to play as well as I can if I'm going to win. But then again, he's going to have to play as well as he can, too.''

Agassi agreed with that.

''He's difficult for everybody,'' Agassi said. ''He's been No. 1 in the world now for almost a full year. He makes you play a great match to beat him. I've just got to come out there and do it.''

Hewitt said at 32 Agassi still plays high-caliber tennis.

''He's in great shape,'' Hewitt said. ''I don't care what age he is. He looks as fit as ever to me. He looks stronger than he's been probably in the past as well and you know I can't recall too many matches that Andre's lost because of his fitness.''

Hewitt said Agassi hits the ball clean and has improved on his serve, using it to wear down opponents. That was just what happened to Mirnyi, who played at a high level and gave Agassi some problems early. But he wound up as just one more victim in Agassi's journey through the final Grand Slam of the season.