American John Isner admits he was surprised after he secured the biggest title of his 14-year career on Sunday when he won the Miami Open by overcoming Alexander Zverev.

The 32-year-old had endured a tough start to the 2018 campaign after just two wins all season.

However, he showed signs of his best tennis as he helped the United States secure their first clean sweep at Key Biscayne since 2004.

Andy Roddick and Serena Williams were the last two to win both the men’s and women’s events, and Sloane Stephens had earlier enjoyed another final win.

German fourth seed Zverev had been hoping to collect his seventh ATP Tour title but was unable to get the job done.

He claimed the first set after blocking five break-point chances but Isner showed plenty of determination to win.

Isner eventually secured a 6-7 (4-7) 6-4 6-4 comeback victory in two hours and 29 minutes to land his maiden Masters title.

He told reporters: “I couldn’t have scripted this. I came into this tournament, I won one ATP [World Tour] match all year and was playing very poorly.

“I won my first match in three sets and that’s how tennis goes – you start to gain a little confidence and next thing you know things start to roll your way.”

Isner, who had his three previous major tour final appearances in 2012, 2013 and 2016, will become the top-ranked American and move up to ninth in the new world rankings.