John Isner has come from a set down to beat Juan Martin del Potro in the semi-finals of the Cincinnati Masters.

Del Potro looked the stronger player in the first set and almost managed a break in the seventh game, but Isner held on to claim it.

There was no separating the pair, so the opening set went to a breaker which Del Potro claimed 7-5 despite being 5-4 down.

Del Potro again threatened the Isner serve, this time in the fourth game but the American held on once more for an important hold.

The Argentine did break at the perfect time to go 5-3 up to claim and had a match point on his serve, but Isner rallied to break back and eventually claim the set on an 11-9 tie-break.

In the decider, Isner broke to go up 3-0, from which Del Potro was unable to battle back with the American moving on to face Rafael Nadal or Tomas Berdych.