He also quit at the 2006 and 2007 French Opens at the third round and quarterfinal stages, respectively, while at the 2009 Australian Open, where he was defending champion, he pulled out of his quarterfinal with Andy Roddick citing heat exhaustion.
The second set immediately saw the Argentine under pressure on his serve, and though he managed to fend off Djokovic in game one, the relentless pressure told in game three as Del Potro sprayed two forehand errors to lose serve again.
When asked if the 31-year old Serbian could break Federer's record, Del Potro sounded quite confident as he said, "Of course he can". In fact, the 95-minute second set in the final was a microcosm of Djokovic's last two years.
It is the third U.S. Open title of Djokovic's career, and his 14th overall Grand Slam win. Nadal, Federer and Djokovic last occupied the top three spots in the rankings in April 2015. It's the Serb's 14th career Grand Slam singles title-tying Pete Sampras for third all time-and his second consecutive major win, as he triumphed at Wimbledon just two months ago.
Del Potro said he was most proud of not giving up in pursuit of another Grand Slam final, adding: "I got it after nine years, which is awesome to me because the US Open is my favourite tournament and I'm proud of that".
"I can't believe she managed to get all the way up", Djokovic said. Her grandfather, who lives in Nemuro, Hokkaido, expressed his joy, saying, "I want her to make a spectacular showing at the 2020 Tokyo Olympics, too".
In the tennis wilderness following an elbow injury and loss of motivation, Djokovic has now won two straight Grand Slams following his success at Wimbledon.
On the other hand, Del Potro was relying heavily on his serves and power.
For quite some time after that Djokovic looked towards Del Potro's singing friend with utmost anger, unable to get them out of his head and that showed on the court.
The nine-year gap between his first and second Grand Slam finals is the longest ever in the men's game.
The three-time US Open victor said his hike in France had given him a fresh perspective on life. Del Potro would not rue how many of those could have been his had he been injury-free all those years.
While Simona Halep of Romania retained her top spot on the list, Germany?s Angelique Kerber moved one spot up to acquire the third position.
The tiebreaker was resolved thanks to more del Potro miscues on his forehand side, as he looked more and more worn out.
But in that critical eight deuce game, the three break chances evaporated.