The last time Del Potro and Federer played was past year in the Basel final where Federer won 6-7 (5/7), 6-4, 6-3. "I'm still surprising myself, and I want to keep surprising the tennis tour". This moment is so big for me because I've never won a title like this.
Federer is 290-points ahead going into the tournament in Miami, but his long-time rival's absence ensures he has a buffer of 890-points as he plays at the second North American Masters Series event.
"It was a lot of frustration after that match point, but then I play well", del Potro said.
In the third set, Federer had the opportunity to serve for the match, holding two match points of his own, however del Potro was able to hold off any title-winning celebrations that the 36-year-old Swiss had foreseen to force deuce - before eventually securing the break.
After slipping outside the world's top 400, Del Potro returned to the top five in 2013 but another wrist injury meant more surgery and led him to miss the majority of the 2014 and 2015 season.
Del Potro was tipped as a future world number one in 2009 after the then 20-year-old reached the French Open semi-finals, the Australian Open quarter-finals before capturing his maiden Grand Slam at Flushing Meadows.
The new Indian Wells Masters champion Del Potro has climbed two places in the rankings with Dominic Thiem and David Goffin dropping down.
He saved three match points and blew one of his own as he snapped Federer's 17-match streak this year.
The Swiss maestro served for the set, and the title, but del Potro dug deep to save three match points, two at 40-15 down, before breaking back to send the stanza to a tiebreak, which the Argentine dominated.
Beating Federer has never been easy - del Potro had succeeded just six times in 24 previous attempts - and the nailbiting final lasted nearly three hours with both players taking occasional issue with the chair umpire.
It was a see-sawing match with brilliant tennis from both players and fistfuls of tension throughout.
Del Potro and Osaka each earned $1.3 million.
It was then Del Potro's turn to rue a missed opportunity, dumping his usually reliable forehand into the net as he went for the victor on match point.
"I love to play against him", Del Potro said. He closed out the win on his third match point when Federer's forehand failed. We enjoy that. And also it was tough and fair on the court.
He said: "I'm so happy to be back in the final here in Indian Wells".
"So it should sting, like you said, for a bit".