Heraldo de Madrid - Zverev shakes off recent funk to beat Muller in Munich

The German came into the Munich tournament having lost his opener at last week's Monte Carlo Masters to Italian Matteo Berrettini, missing the chance to bump Jannik Sinner from the world the No 1 position.

Instead, that defeat and the Carlos Alcaraz's victory in the final on Sunday saw Zverev dropping down a place in the rankings and dented his preparations ahead of next month's French Open.

Zverev broke his opponent in the first game but Muller broke back at 3-3 before Zverev recovered to win the set in 47 minutes.

The number one seed found his rhythm in the second, breaking his opponent three times.

The 27-year-old completed victory in one hour and 20 minutes.

Clay-court specialist Zverev has played six tournaments since losing the Australian Open final in three sets to Sinner in January, but has not made it past the quarter-finals at any.

Since winning back-to-back titles in Munich in 2017 and 2018, Zverev has not made it past the final eight.

He will face either countryman Daniel Altmaier or Taiwan's Tseng Chun-hsin in the quarter-finals.

Earlier on Monday, world number 15 Ben Shelton endured a stuttering start to the tournament, coming from a set down to beat world number 410 Borna Gojo 4-6, 7-6 (8/6), 7-6 (7-3).

Shelton, seeded second in Munich, fought off three match points, winning both of his sets via tiebreak in two hours and 24 minutes.

Defending champion Jan-Lennard Struff, who beat American Taylor Fritz in the final last season, opens his campaign against Argentinian Francisco Cerundolo on Tuesday.

A.Montoya--HdM