(CNN) - For Roger Federer it was one of those few occasions when a final got away from him.
In 2009, the now 19-time grand slam champion lost in five sets to Juan Martin del Potro -- then only 20 -- in the US Open final. The two players will meet again in the quarterfinals on Wednesday.
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"The only time when he was really better, in my opinion, was the fifth set," Federer told reporters as he looked back on his 3-6 7-6 (7-3) 4-6 7-6 (7-4) 6-2 defeat seven years ago.
On Monday, Federer cruised past Philipp Kohlschreiber 6-4 6-2 7-5 but his thoughts quickly turned to his match with Del Potro.
"It probably feels like one of those matches I would like to play over again," added Federer, referring to the 2009 final.
"I feel like I would probably win it somehow because I should have been up maybe 2-0 or should have been up 2-1.
"It was a good match. A lot of back and forth. Crowd was really into it. Started in the day, finished in the night.
"I was not too disappointed I don't think because I had a great run, you know, winning I think the French, Wimbledon and then the birth of my girls."
Del Potro's success in 2009 also ended Federer's five-year winning streak at the US Open, though the Argentine then suffered a series of injury problems -- he has had to undergo four wrist surgeries.
On Monday, del Potro rolled back the years saving two match points before going on to defeat Dominic Thiem 1-6 2-6 6-1 7-6 (6-1) 6-4.
The Argentine enjoyed huge support -- chants of "Del-Po! Del-Po!" frequently rang out -- as Del Potro, who has been struggling with flu symptoms, reached the US Open quarterfinals in New York for the fifth time in nine appearances.
"I played one of the epic matches of my career here in the US Open, which is my favorite tournament, in front of a great crowd," said Del Potro speaking after his win on Monday.
"I was exhausted after the last point of the match. But I'm so glad to go through. I played a fantastic battle against one of the best players on the tour.
"I was thinking to retire in the middle of the second set because I couldn't breathe, I couldn't move well. Dominic was dominating the match so easily. But then when we started the third set, I broke his serve very quick, and then I won the set in 20 minutes.
"Then the story changed a lot. I started to see the crowd. I took all the energy from the fans. That's what I did in the end, just keep fighting. I didn't give up on any points from the third until the fifth set. I was ready to win the match in that moment."
Looking ahead to Wednesday's meeting with Federer, Del Potro said it was going to be an "interesting" match to play.
"I know how to play if I want to win, but always is a pleasure to play the greatest guy in history."
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