Alexander Zverev came from a break down in both sets to defeat Marin Cilic 7-6 (5), 7-6 (1) at the ATP Finals on Monday.

Facing each other in their opening match for a second straight year, Zverev produced the slightly steadier tennis in an error-strewn contest to extend his record against Cilic at the O2 Arena to 2-0.

The fifth-seeded Cilic broke at the first opportunity for 2-0 but then wasted break points in the German's next two service games, before dropping his own serve when attempting to close out the set at 5-3.

Having struggled to that point, the third-seeded Zverev found some consistency to take the tiebreaker.

In the second set, once more fell he behind at 4-3.

However, Cilic, who amassed 46 unforced errors, allowed Zverev to break straight back.

Despite saving a match point at 4-5, Cilic wilted in another tiebreaker to fall to 1-9 across his four appearances at the tournament.

In the late match, top-ranked Novak Djokovic begins his campaign for a sixth ATP Finals title against American debutant John Isner.