After missing out on a match point in the second-set tiebreaker on Sunday, Del Potro had to fight back from a break down against the defending champion and current world No. 1 to win, 6-4, 6-7 (8), 7-6 (2).
Never short of fighting spirit even when his joints were unable to back it up, del Potro saved three match points and blew one of his own on the way to a victory that snapped Federer's 17-match winning streak this year. "I can not believe I won this tournament, beating Roger in a great final and level of tennis".
World number eight Del Potro is back in the rankings top 10 after dropping to 1,045th before beginning his comeback from three left wrist surgeries in 2016.
"I'm excited to keep surprising myself, the tour and seeing what I can do".
"I'm so happy to win a title like this. We played great tennis today", Del Potro said.More news: Tamil Nadu: Another Periyar statue vandalised, this time in Pudukottai
Del Potro claimed a stunning four-set win over Federer at the US Open in September past year, but Federer won their last meeting in Basel a month later.
"The first thing is try to be healthy during the whole year and play where I like to play".
Federer hasn't started a season so well since 2006, when he won his first 16 matches en route to a 92-5 record.
Roger Federer was on the ropes, down two breaks in the second set and another one in the third. "Well done. Enjoy the moment", Federer said.
However, del Potro can now drive his backhand effectively with two hands again without having to rely on a one-handed slice.
With Federer on top 6-5 in the second set tie break, he appeared to fire an ace to clinch the set, but a late challenge by del Potro overturned the call and the Swiss was double faulted.More news: Putin finally gets a phone call from Trump
And in the tiebreak, the Swiss star's forehand went AWOL as he lost the breaker 7-2 to the Argentine, who won at an ATP Masters 1000 event for the first time.
He took two hours and 42 minutes to win the match. But for all the camaraderie, this was pure, intense competition and also a particularly fine tennis match, filled with winners on the run, drop shots and phenomenal fast-twitch defence from Federer as he repeatedly half-volleyed del Potro's huge shots from the baseline or closer to the net.
Federer and Marin Cilic are the top two seeds, the three-time victor getting his campaign under way against a qualifier while the Croatian will face either Pierre-Hugues Herbert or Taylor Fritz.
"I always play good against him".
"It had no effect on the outcome of the match", Federer said.
"I see the positives at the end of the day".More news: US Doesn't Congratulate Putin Over 'Unsurprising' Election Win
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