Now he's backed that up at the U.S. Open, the fourth time in his career he won multiple majors in a season. "(His) decisions were in accordance with the relevant rules and were re-affirmed by the US Open's decision to fine Serena Williams for the three offences". Del Potro would not rue how many of those could have been his had he been injury-free all those years.
Djokovic was better than del Potro on their many lengthy exchanges, using his trademark body-twisting, limb-splaying court coverage to get to almost every ball, sneakers squeaking around the blue court in Arthur Ashe Stadium, where the roof was closed because of rain. But also I think we are proud to be close to these legends.
For Djokovic, he got better as the tournament progressed.
Throughout the tournament, the two struggled and rose above New York's searing heat and hard humidity.
Djokovic had tumbled down the rankings, slowed previous year by an elbow injury and a loss of confidence that accompanied a 54-week title drought.
When another forehand error cost Del Potro his serve early in the second, all the momentum was with Djokovic.
Djokovic and Del Potro began the match judging each other's moves and holding their serves comfortably. 1 and 2, respectively, while Germany's Angelique Kerber climbed one place to 3.
The second set was a physical one as the two players were on the court for 95 minutes.
The eighth game was an epic, lasting over 20 minutes and featuring eight deuces before Djokovic withstood the pressure to hold.
The tournament, meanwhile, set a new attendance record of 828,798 fans through the gates at Flushing Meadows.
"I love Serena, first of all", Djokovic said. And it all started with Djokovic getting erked by crowd reaction and constant singing for Del Potro.
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That means he will have played only 24 tournaments this year, which includes the Ryder Cup. Rory McIlroy finished fifth at 18-under after firing a final-round 2-under 68.
Ironically, John McEnroe, who quarreled with umpires throughout his career, presented Djokovic with the trophy. But nobody represents the modern-day game as well as Djokovic.
In the middle of that there was some world class tennis on display.
The end was near and when Djokovic put away a smash on a first match point, he fell onto the court on his back. Twice, the Serb tried to attack at the net.
Del Potro was convinced Djokovic, who will return to the top five in the rankings, could overtake the iconic duo. Djokovic was able to win the tiebreak 7-4 to secure a two-set lead.
In the tiebreak, Del Potro looked susceptible to forehand errors and Djokovic showed huge courage and quality to take it away from Del Potro, going up 2-0 in the final.
Djokovic was soon 3-1 up in the second set before Del Potro carved out his first break point of the match to level at 3-3.
"Ever since then, the tennis is completely different for me". But winning at Ashe is as big as it gets.
Djokovic said he believes del Potro will win another major title.
To his credit, Del Potro rallied again to recover a break in the third set, but Djokovic was simply too good and sealed the match with a smash before collapsing in delight.
It comes seven years after the New York Times revealed top chair umpires were skipping the US Open because of how poorly it paid officials.