On Sunday, he did so for the third and fourth time, respectively, as he triumphed over Isner 3-6, 6-1, 6-2 at Rock Creek Park.
Isner began the match strong, hitting serves clocking in as fast as 135 mph. Nonetheless, it was clear as the second set progressed that Isner was losing his legs while del Potro had plenty of gas left in the tank.
The 24-year-old Argentine’s endurance ultimately proved to be his strongest weapon against his 6-foot-10 opponent.
Del Potro, meanwhile, had to fight fatigue early in the match after waiting out a three-hour rain delay before defeating Tommy Haas in Saturday’s semifinals.
“I think it was a little frustrating to finish so late last night,” del Potro said. “[Isner] had more time to prepare for the match. I needed to focus on the match and play the best I could. I think I was improving game by game. … In the end, I hit really good strokes with my forehand. I was solid for the last two sets of the match.”
A major turning point came midway through the second set when Isner was presented with an apparent overhead spike “gimme.”
“When the match was going, I started feeling better, I started to run more,” del Potro said. “I found a way all the time with the low rallies and felt good by the end.”
NOTE: Magdalena Rybarikova defeated Andrea Petkovic 6-4, 7-6 (2) in the women’s Citi Open final.