Top-seeded Juan Martin del Potro of Argentina relishes winning the Citi Open for the third time after his 3-6, 6-1, 6-2 victory over eighth-seeded John Isner. del Potro also won the event in 2008 and ‘09; Isner also was a finalist in 2007. (Jewel Samad/AFP via Getty Images)

Having not played John Isner in two years, it took Juan Martin del Potro a while to adjust to the hair-raising speed and peculiar trajectory of the 6-foot-9 American’s serve.

But once del Potro figured it out, abandoning his initial strategy of fielding the blasts from the baseline and retreating to nearly the spectator seats at William H.G. FitzGerald Tennis Center, the Argentine steamrolled to his third Citi Open championship, 3-6, 6-1, 6-2.

Washington’s hard-court classic was del Potro’s first tournament since a gutting, five-set semifinal loss to top-ranked Novak Djokovic at Wimbledon last month. After seeing the caliber of the players in the Citi Open’s 48-player draw, del Potro dismissed any thought of winning the title in his first test after the extended break.

But the top seed improved with each round. And by Sunday, despite getting to bed at 3 a.m. following a Saturday semifinal that stretched past midnight, del Potro manhandled Isner, who ran out of energy and tactics roughly 30 minutes into the match.

Del Potro’s victory, wrapped up in 89 minutes, proved that there is more to being a dominant player than height and a big serve. It also demonstrated that the gap between the world’s No. 7 and No. 20 players is considerable.

Isner, whose career record against del Potro fell to 0-4, had no trouble conceding the point, characterizing the Argentine as “one of our game’s greatest players” and his forehand as arguably the best in the world.

A Greensboro, N.C., native, Isner arrived in Washington as the game’s hottest hard-court player, fresh off a victory in the preceding week’s tournament in Atlanta. Entering Sunday’s final against del Potro, he boasted an eight-match winning streak and had been broken only once in his last four matches.

After struggling through the first set, del Potro broke the American four times and, in one brilliant stretch, reeled off seven consecutive games.

“Isner’s serve is so difficult to return,” said del Potro, 24. “I start returning on the baseline, and I couldn’t [get] to any. So I go almost out of the court to take the ball, and I started to return well. But it took like an hour, or one set and a half, for me to see the returns.”

Isner, seeded eighth, opened the match by blasting an ace.

And del Potro looked a step slow, with the whipping wind making Isner’s serve only trickier to anticipate.

The Argentine was broken in the fourth game by the bad luck of a net cord, which caught a forehand volley headed toward the open court and plopped it back on his side of the net. That one break was all Isner needed, and he served out the set with a 137 mph blast.

At 6-6, del Potro himself is among the sport’s taller players. But the rangy Isner and his 238-pound frame had started wearing down from the pounding of playing so many matches in two weeks. Sunday’s was his ninth in 11 days.

The fatigue started showing in the second set. Meantime, del Potro switched his service-return tactics and ramped up the pace of his groundstrokes. He also sprinkled in drop shots and occasional forays to the net to keep Isner off-balance.

He broke the American twice in the set — once at love. And he raised his level of play still higher in the third set, while Isner looked alternately sluggish and impatient, spraying groundstrokes that were intended to win points quickly but instead sailed long and wide.

From 1-1 in the second set, Isner didn’t win a game until three games into the third set. Down a break by then, he was broken yet again in the seventh game.

Del Potro was in full command. Even Isner’s vaunted serve didn’t bother him.

In his semifinal victory over unseeded Dmitry Tursunov, Isner blasted 29 aces. But against del Potro, he managed only six.

Serving at 5-2, del Potro crushed a forehand winner with such pace that Isner didn’t even try for it. And on match point, del Potro ripped a backhand crosscourt with the same fury.

With the season’s final major, the U.S. Open, looming just three weeks away, Isner was asked what he thought about del Potro’s prospects. One of the rare South Americans to prefer hard courts to clay, del Potro won the U.S. Open in 2009 shortly after capturing his second Citi Open title in a row.

Isner placed him third — “maybe just the smallest hair behind a guy like Djokovic and [Andy] Murray” — which amounts to high praise, indeed.

“I wish I felt a little bit better out there,” said Isner, 28, now a two-time runner-up in Washington. “At the same time, I could have been 100 percent and clicking on all cylinders and still not have won that match. That just speaks to how good a player he is.”

Note: Earlier Sunday, the unseeded tandem of Julien Benneteau of France and Serbia’s Nenad Zimonjic won the men’s doubles title, 7-6 (7-5), 7-5, over American Mardy Fish and Radek Stepanek of the Czech Republic. Benneteau and Zimonjic won all four of their matches in the tournament in straight sets.