John Isner beats Grigor Dimitrov in Miami Masters

John Isner is through to the fourth round of the Miami Masters, thanks to a straight-sets win over Grigor Dimitrov.

The Bulgarian struggled to cope with Isner's powerful serve in the first set, and a tie-break looked likely from the opening game.

The American upped his performance in the tie-break, and forced a couple of Dimitrov errors with some fine ground strokes to take the set 7-6.

Isner capitalised on his momentum at the beginning of the second set with an early break of serve, and a Dimirov double-fault handed him a second break a few games later.

An ace down the middle confirmed victory for Isner, who will meet Milos Raonic in the next round.