Juan Martin del Potro defeated Roger Federer 5-7, 6-3, 6-7, 6-4 in their US Open quarter-final, but admits he got ‘lucky’ at a key moment in the match.

Eight years after he won a five-set thriller against Federer in the final, Del Potro came out on top again in Flushing Meadows.

The Argentinian was happy with his performance, but admits it could have been a different story.

The third set had to be decided by a tiebreak, and in that crucial moment, Federer failed to convert four set points before Del Potro eventually managed to take it 11-9.

That mini victory did wonders for Del Potro's confidence and things went his way in the fifth, but he admits he was 'lucky' to get away with a double fault at 6-6 in that tiebreak.

"Well, I think I played my best match of the tournament. I did everything well,’ he said to the interviewer right after the win.

"I served so good, I hit my forehand as hard as I can and I think we played a great match and I deserved to win in the end.

"I don’t know, I think I got lucky.

"I made a double fault at 6-6 and that cannot happen against Federer but in the end I got lucky and I made good returns, good slices and in the fourth set I played even better."

Del Potro's last obstacle before the final is Rafael Nadal - world's number one and a well-known opponent. But, the Argentinian keeps some good memories and hopes he can repeat the story.

"Well I played him in 2009 too, the same as Roger, and hopefully I can achieve the same result," he continued.

Del Potro then expressed his appreciation to the supporters, who drove him forward and made him 'feel happy' after all the difficulties he has been through.

"We look older but Rafa is playing a great season. He’s number one in the world but with this amazing support, everything can happen.

"You make me feel happy every time when I play here and I love your support, guys.

"I love to see you in the crowd cheering for me, chanting for me, hitting harder my forehand at the same time as me and I know against Rafa the crowd will be tough for me but I hope you are there cheering for me again.

"I cannot believe I get to play another semi-final after all my injuries, after all my surgeries and especially to play here in New York, it’s great, it’s my favourite tournament, my favourite city to play tennis."