Alexander Zverev was pushed to the limit in the opening round of the Munich Open as he defeated Miomir Kecmanovic in three sets.

The first 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 third seed 6-4 6-2 in just 65 minutes.

Data Debrief: Zverev impresses at the net

Zverev, who is searching for a record fourth title in Munich, benefited from more aggressive shots against Kecmanovic.

The German won 85% of his net points (11/13), while he also fired in 12 aces compared to Kecmanovic's one.

Elsewhere, world number 166 Molcan registered his first victory over a top 20 player in three years with his win over Bublik.