WATCH the Munich Open LIVE in Australia on beIN SPORTS | Subscribe here and take advantage of our 7-day FREE TRIAL

The No.1 seed and reigning champion won 6-3 3-6 7-6 (7-2) in two hours and 21 minutes to set up match in the last 16 with Gabriel Diallo.

The pair exchanged breaks early in the first set before Zverev broke once more in the sixth game to win the opener.

Zverev looked to be on his way to a routine win when he got the better of Kecmanovic's serve in the first game of the second, but the Serbian broke back immediately.

Kecmanovic then saved a break point in a mammoth fifth game before converting a break point opportunity of his own to force a deciding set.

Neither player lost serve or even gave away a break point in the third, but Zverev's quality came to the fore in the tie-break as he clinched victory with his first match point.

Joao Fonseca also booked his place in the last 16 in Munich with a 7-6 (7-1) 6-3 win over Alejandro Tabilo, with the Brazilian facing Arthur Rinderknech in the next round.

Alexander Bublik, meanwhile, was stunned by qualifier Alex Molcan, who defeated the No.3 seed 6-4 6-2 in just 65 minutes.