ATP Finals: Zverev begins with Cilic victory

On a quick, bouncy surface, Zverev dealt with the big moments better in a match that saw 80 unforced errors and several swings in momentum. 

After coming back from a break behind in both sets in Monday's Guga Kuerten group match, Zverev's chances of bettering his group stage exit last year are good.

"It's tough to play against him," said the 21-year-old of Cilic after the match. "I knew that I wanted to fight back from every score and I did that, I’m very happy."

Zverev forced himself in to a comeback earlier than he would have hoped with a string of overhit forehands handing Cilic a 3-0 lead and causing the German to hurl his racquet to the ground in frustration.

The Croatian player looked much more comfortable in the 02 Arena and had the chance to wrap up the opener at 5-3. But, out of the blue, Cilic produced three unforced errors before a double fault handed a break, and the inititative back to Zverev.

With his confidence boosted by his opponents' errors, Zverev took the lead for the first time since the opening game in the first point of the tie break and, despite missing two chances on his own serve, finally converted a classy backhand after bringing Cilic to the net.

Usually so strong, Cilic's serve was letting him down but he clung on in the early part of the second set before taking advantage of a poor game from the third-seeded German in game seven to seize control of the set.

True to the rhythm of the match, the number five seed soon relinquished that control, with an error-strewn in game eight that restored parity.

Zverev missed the contest's first match point in the next game as Cilic's serve consistency started to return, sending the players to another tiebreak. Again the German took command, this time with a series of punishing groundstrokes before a Cilic second serve was incorrectly called out, but the 30-year-old had already used all his challenges.

A brilliant backhand down-the-line followed quickly by a serve that proved too hot to handle wrapped up a straight sets victory for Germany's brightest tennis prospect. He'll play Novak Djokovic on Wednesday, with a win almost certain to conform a last four spot.