Top seed Roger Federer reached the quarter-finals of the Rome Masters with a 7-6 6-3 victory over Ivo Karlovic.

A tie-break was required to decide the first set after Federer failed to convert five break point opportunities.

On each occasion Karlovic used his serve to escape trouble, but the 6ft 10inch Croat finally cracked in the tie-break, losing 7-4.

Federer secured the first break of the match in the fifth game of the second set and broke again in the ninth to take the set 6-3 and complete the win.

The world number one faces Radek Stepanek in the last eight after the Czech beat Peruvian qualifier Luis Horna 6-4 1-6 6-3.