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It was the German's first title of the season, but his 24th on the ATP Tour, and the victory moved him above Carlos Alcaraz to No.2 in the world rankings after the Spaniard was upset in the Barcelona Open final by Holger Rune.

“It’s extremely special, I always love winning tournaments in Germany,” Zverev, who earned his first title of the season, said.

“It’s probably the most special thing I can do. It’s definitely a great birthday present, let’s put it that way.”

American Shelton was shaky on his service games in the opening set, coughing up break points at crucial times in the first and seventh games.

At the other end, Zverev dropped just three of 19 points as he confidently took the first stanza.

Zverev continued the onslaught in the second set, opening it with another break of Shelton's serve, and that was enough to see him to a ninth title on clay.

“I definitely knew I had to play my best tennis today, Ben has been playing extremely well this week,” Zverev said.

“The conditions suit him extremely well, it’s very hot and very fast. They suit me as well, to be fair. I enjoyed my birthday so far.”