Juan Martin del Potro believes US Open champion Novak Djokovic can become the most successful male tennis player in Grand Slam history.
Since collecting an unexpected Wimbledon title Djokovic has gone from strength to strength, adding a long-awaited Cincinnati Masters title to his resume before adding the US Open title to those he won in 2011 and 2015 and matching Pete Sampras' mark of 14th Grand Slam titles and leaving him three behind Rafael Nadal and six adrift of Federer.
Playing in his eighth US Open final, the Serb delivered a businesslike 6-3 7-6 (7-4) 6-3 victory over third-seeded Del Potro.
Djokovic is nearly six years younger than Federer and prior to a two-year barren spell, he had been winning slams at an average of nearly two a season.
Asked if he can catch Federer, Del Potro said: "Of course he can. He has 14 already. He won two grand slams in one year. He's healthy. He has a great team working with him.
"Hopefully him, Rafa, Roger are still fighting for Grand Slams, because it is so nice to watch them fighting for history. We just do what we can against them. But Novak has everything to make records in this sport."
Between them, Federer, Nadal and Djokovic have won 47 of the last 55 slam titles, but taking into account all Del Potro's wrist injury problems he was back in a Grand Slam final for the first time in nine years.
And he has no regrets, saying: "It is a big challenge to take these kind of tournaments from them. But also I think we are proud to be close to these legends.
"I've been - during all my career - learning with Novak, Roger, Rafa, seeing them winning these events very often. It's amazing. I don't feel sad that I couldn't win grand slams because of them. I am just one of the guys that is lucky to be in the same era as them."
Del Potro cried for a long time after the match and admitted the defeat will be difficult to get over.
He said: "I think I did a good tournament, but this is a tough loss for me. I'm really sad to lose the final in this tournament because I had too much passion playing the final, trying to win the title again.
"I think it's time to take a break, to see how my body feels for the future, and then be ready for the next one."
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