The No.2 seed, who is looking to follow up his tournament win in Madrid by retaining his title in Rome, extended his unbeaten run to 13 matches with a hard-fought 7-6 (15-13) 7-5 victory.

Cilic played his part in a compelling tussle but failed to make the most of his opportunities, particularly in a lengthy tie-break to decide the outcome of a tight opening set.

The big-serving duo matched each other all the way before Zverev eventually came out on top, but not before he lost his cool after a debatable call.

After smashing his racket in frustration, the German quickly regained his composure, taking the set when some excellent defensive work led to his opponent dumping a shot into the net.

The Croatian responded to the disappointment with an early break in the second, yet Zverev bided his time before drawing level in the eighth game.

He went on to clinch the win with a backhand down the line as he came up to the net to meet a drop shot, sending the ball beyond a stranded Cilic to settle the contest after just over two hours on court.

Nadal had triumphed earlier in the day, overcoming Novak Djokovic 7-6 (7-4) 6-3 to increase his chances of taking over from Roger Federer at the top of the world rankings.