KEY BISCAYNE, Fla. – John Isner punctuated his unexpected run to the Miami Open title with a surprising display of agility, dancing across the court while basking in a breakthrough.

The 6-foot-10 Isner looked twice as tall skipping about with a grin brighter than the Florida sunshine. He had just won the biggest title of his 14-year career, holding every service game and rallying past Alexander Zverev 6-7 (4), 6-4, 6-4 on Sunday.

Isner, who turns 33 this month, previously had been 0-3 in ATP Masters 1000 finals.

“You can’t replicate moments like this,” Isner said during the trophy ceremony. “I’m toward the latter part of my career; this is the best moment of my career.”

Isner’s win came in the last singles match on Key Biscayne before the Miami Open moves next year to the NFL Dolphins’ stadium.

Seeded 14th, Isner became the first American man to win the tournament since Andy Roddick in 2010. Isner joined Sloane Stephens , who won the women’s title Saturday, for the first U.S. sweep in the event since 2004, when the champions were Roddick and Serena Williams.

The start of the last game was delayed by the crowd’s chants of “U-S-A!” Isner then held at love, and on the final three points he smacked aces, giving him 18 for the match and 79 for the tournament.

“I was just ready for this moment,” he said. “I’ve been here three other times, and I’ve lost three times on this stage. I was just ready for it.”

Isner is best known as tennis’ marathon man thanks to his 70-68 fifth-set victory over Nicolas Mahut at Wimbledon in 2010. He possesses perhaps the game’s biggest serve but has never reached a Grand Slam semifinal, largely because a lack of mobility makes it difficult for him to stay in rallies.

The string of victories on Key Biscayne surprised even him because he arrived with a record of 1-6 this year, including losses to players with rankings of 60, 62, 78 and 91.

“I couldn’t have scripted this,” Isner said. “I was playing very poorly. But that’s the way tennis goes. You gain a little confidence, and things start to roll your way.”

He played an almost flawless semifinal to beat Juan Martin del Potro, and was just good enough against the fourth-seeded Zverev, a precocious 20-year-old German who was bidding for his third Masters 1000 title in the past 12 months.

The Key Biscayne finale drew a near-capacity crowd, and the atmosphere was electrifying at times. When Isner hit a forehand winner during a tense final game of the second set, he whirled his index finger as he looked around at the roaring crowd, coaxing the decibel level still higher.

Two points later, when Zverev won a wild exchange with both players at the net, he waved both arms toward the stands, inspiring another crescendo from the fans.

Isner’s serve allowed him to overcome inconsistent returning, a succession of botched volleys and shaky play at crunch time. He converted only two of 12 break-point chances and lost his final three service points in the tiebreaker.

But he gave Zverev only three break-point chances, and Isner’s serve was at its best down the stretch. He made 83 percent of his first serves in the final set.

Meanwhile, baseline errors by Zverev mounted.

“I think I missed more shots today than I did in the whole tournament,” the young German said. “I played bad from the baseline, but it’s not easy against John. You always feel the pressure that if you get broken, you might lose the set.”

Mindful of that small margin for error when he lost serve to fall behind 5-4 in the final set, Zverev let his frustration boil over. He slammed his racket to the concrete, picked it up and slammed it again, and then tossed it gently to the stands as a mangled souvenir.

When Isner sealed the victory four points later, he also tossed his racket – but in celebration. Then it was time to dance.