John Isner has booked his spot in the next round of the Madrid Masters with a 7-5 7-6 victory over a spirited Guillermo Garcia-Lopez on Monday.

Both players demonstrated some of their best tennis in the first set, with Garcia-Lopez twice coming close to breaking Isner in the early stages.

The opening set remained on serve until 5-6, but an Isner break allowed the American to move into a one-set lead.

Neither could be separated in the second, meanwhile, with each player holding their serve with relative ease to force the second set into a tie-break.

Incredibly, in keeping with the rest of the contest, the tie-break remained on serve until 8-9, when Garcia-Lopez was eventually broken by a big forehand, allowing Isner to win it 10-8.