John Isner has battled into the third round of the Italian Open by beating Leonardo Mayer in straight sets.

The 16th seed forced the issue during the opening set, but he squandered three break points before failing to convert a set point at 5-4.

Isner then had to defend a set point in the tie-break as Mayer looked like he was going to land the first blow, but the American kept the Argentine at arm's length on his way to taking it 7-6(6).

The world number 17 moved into a 3-1 lead at the start of the second, and his trademark big serve remained steady after that as he clinched the contest 7-6(6) 6-4.

Isner will now play either seven-time champion Rafael Nadal or Marsel Ilhan for a spot in the last eight.