German world No 3 Alexander Zverev is through to the quarterfinals of the ATP event in Munich after cruising to a straight-sets win over Daniel Altmaier on Wednesday.
Zverev, the top seed at a tournament he won in 2017 and 2018, won 6-3, 6-2 in 79 minutes, reaching his 99th quarterfinal on the ATP tour.
Zverev has not made it past the quarters on the Munich clay since last winning the tournament seven years ago. He has also struggled for form since losing the Australian Open final in January.
In six tournaments since losing to Jannik Sinner at Melbourne Park, Zverev has been unable to get past the quarterfinals.
A defeat to Matteo Berrettini in his first match at the Monte Carlo Masters last week cost Zverev a shot at the world No 1 ranking.
The 27-year-old will face either fellow German Yannick Hanfmann or Tallon Griekspoor, of the Netherlands, for a place in the semifinals.
Zverev joined world number 15 Ben Shelton in the last eight. Shelton beat Botic van de Zandschulp 7-6 (7/1), 6-3 earlier on Wednesday.
Shelton, seeded second, was broken in the opening set by Van de Zandschulp, in the tournament as a lucky loser.
The American fought back with a break of his own before a dominant showing in the tie-break.
The 22-year-old continued his dominance in the second set, winning the match against his 89th-ranked opponent in one hour and 28 minutes.
"I couldn't be happier," Shelton told the crowd. "I love playing in Germany and especially in Munich... there's still a lot to do."
Shelton will face Italian Luciano Darderi in the quarterfinals.