John Isner fought back from a set down to claim the biggest title of his career at the expense of Alexander Zverev in the last Miami Open final to be played at Crandon Park.

Isner produced another outstanding exhibition of serving to become the oldest player to win a first Masters tournament, beating the fourth seed 6-7 (4-7) 6-4 6-4 in his homeland on Sunday.

The 32-year-old completed an American double after Sloane Stephens took the women's title on Saturday, seeing off Zverev in the final match at the famous Key Biscayne venue before the event relocates to the Hard Rock Stadium.

Isner fired down 18 aces and did not allow Zverev a solitary break in a gripping battle, the 20-year-old German missing out on a third Masters title after suffering a first loss in four meetings with the 14th seed. 

Zverev dug himself out of a hole in his first service game, with Isner left to rue missing a straight-forward volley at the net as three break points came and went.

Isner saved a break point and Zverev held to level it up at 3-3 after his towering opponent was unable to win another two, the two-time Masters champion then rallying from a mini-break down in the tie-break to take the opening set.

Both players had their serves firing in the second before Isner had the first break-point opportunity in the ninth game, which he grasped by unleashing a brutal backhand that clipped the line.

A pumped up Isner had the crowd on their feet by winning an epic point with an excellent forehand down the line in a high-quality game that the American won to level the match after saving two break points.

Isner saw another five chances to break come and go in tense decider before his persistence paid off when Zverev thudded a backhand into the net, prompting him to demolish his racket in a fit of rage. 

The home favourite held it together to seal the title with a hold to love, winning it with yet another ace on a glorious afternoon in Florida and will move back into the top 10 in the rankings on Monday.