The clay-court specialist Monaco, who triumphed on the red dirt in Vina del Mar in February, secured another ATP 250 crown thanks to a 6-2 3-6 6-3 win over in-form Isner.

Despite the defeat, Isner becomes the top-ranked American player as he climbs to ninth in the world, leapfrogging compatriot Mardy Fish who was ousted in the second round.

Monaco, who lost both of their previous meetings on hard court, coped with Isner's main weapon, his serve, impressively to break twice in the first set on his favoured surface.

The American's serve was far more effective in the second as he recorded five of his eight aces and levelled matters with a solitary break.

Great moment

However, it was the Argentinian who claimed the only break in the decider at 4-3, before serving the match out to secure the fifth title of his career and a career-high ranking of 13.

Monaco said: "I think we played a great final. The first set, I played really well, and then he came back in the second set.

"In the final set, it was a battle. We fought until the last point. I served pretty well in the last game, so I'm happy for that."

He added: "This is a great moment in my career. I've worked very hard to be here. I have the claycourt season in Europe now, which is very important for me. This tournament is going to bring me a lot of confidence."

Isner was left ruing a slow start, saying: "I came out of the gates slow. I wasn't quite there. It took a while to get warmed up and engaged in the match.

"I got better as the match went on. After the first set, the quality from both of us picked up a lot. I had some things go right in the second set. I saved a number of break points. But I had some things go against me in the third set.

"He was pressuring me pretty well all day. All in all, it was a good effort and was the best match I played all week. That's encouraging. I was a little tired, but I didn't feel it at the end."