Andre Agassi produced one of the most incredible comebacks in his US Open history on Wednesday night as he rallied to beat American wild card James Blake 3-6, 3-6, 6-3, 6-3, 7-6 to reach the semi-finals.

The 35-year-old seventh seed trailed by two sets and a break at 3-2 and Blake served for the match at 5-3 in the final set but Agassi snatched the tiebreak 8-6 to set up a clash with another American, Robby Ginepri.

"I never felt like I was going to win this match but somehow I just found the way," Agassi said.

"I could have been off this court in an hour and 20 minutes but I just hung in there somehow.

"I don't think I've ever felt this good here before."

In front of a packed crowd on Arthur Ashe Court, Agassi was outplayed early on by a rampant Blake, who was playing in his first Grand Slam quarter-final.

Ripping forehand winners at will and running down everything, Blake bullied Agassi as he stormed to a two sets lead and broke Agassi's serve to lead 3-2 in the third.

With the finishing line in sight, though, Blake suddenly tightened up and Agassi, the champion in 1994 and 1999, sensed it.

The 35-year-old broke back immediately, won the next three games to take the third set and with Blake visibly tiring, he took the fourth to take it into a decider.

With the crowd roaring him on, Agassi looked the fresher at the start of the final set, but Blake broke in the fifth game and served for the match at 5-3 only for Agassi to play an astonishing game to break back.

The two traded blows to force a tiebreak and again Blake struck first, moving ahead 3-0 but Agassi rebounded to force match point at 6-5.

Blake hammered a forehand winnner down the line to save it, but Agassi then forced another with an audacious drop shot and backhand pass and then clinched the dramatic victory with a winning forehand return.