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Facing an opponent renowned for frequently changing the pace of rallies and producing plenty of craft in his shots, Zverev struggled for his best level at times in the one-hour, 51-minute encounter.

Yet the German also excelled at key moments, and he completed a straight-sets win after saving a set point at 5/6 in the second-set tie-break.

“The first match on grass is never easy,” Zverev said. “I actually think it was a very average match, but I won in the end and that’s the most important thing. I made it complicated, but a win is a win and I’m happy to play tomorrow again.”

Zverev converted four of six break points he earned in his maiden clash with Moutet.

Awaiting Zverev in the quarter-finals in Stuttgart, where he is competing for the first time since 2019, will be Brandon Nakashima. The sixth-seeded American overcame his countryman Learner Tien 7-6(5), 6-3.

There was another home victory earlier in the day when Justin Engel continued his dream run with a 6-4, 6-4 upset of Alex Michelsen. 

The 17 year-old Engel, who had not contested a professional match on grass prior to his first-round win against James Duckworth, broke serve in the third game of both sets to earn his first win against a Top 50 opponent.

Nuremburg-born Engel, who is the youngest quarter-finalist in Stuttgart event history and the youngest tour-level quarter-finalist on grass since Boris Becker won Wimbledon in 1985, has risen 49 spots to No. 232 in the ATP Live Rankings as a result of his run this week so far. 

The German, who is coached by former Top 20 star Philipp Kohlschreiber, is also up four spots to ninth in the ATP Live Race To Jeddah.

Standing between Engel and a semi-final spot is Felix Auger-Aliassime. 

The fourth seed and two-time Stuttgart finalist blunted the big-serving threat of Giovanni Mpetshi Perricard for a 6-4, 6-4 triumph. 

It was the 24 year-old Canadian’s first win on grass since he reached the Halle quarter-finals in 2022.