Zverev and Shelton tested each other in a high-quality encounter before the world No.3 played a near flawless tiebreak to clinch the match in little over two hours on Saturday and stretch his career win-loss record over the American to 3-0.
The 28-year-old banged down 15 aces, 35 winners and did not face a break point in front of his home crowd to reach his first grass-court final in eight years.
"I'm super happy to be in the final, it's my first grass-court final since 2017," Zverev said.Â
"It's been eight years. I actually really like playing on the surface. I'm happy to be in the final in Germany again, I'm looking forward to it."
But in the final, a bigger test awaits Zverev as he tackles Fritz, the American who's beaten him on the last four occasions they've played over the past year.
Despite the defeat, Shelton can take plenty of positives from the ATP 250 event, with the 22-year-old set to make his top 10 debut in the ATP rankings on Monday.
In the first semi-final, Fritz, ranked seventh in the world, sent down 10 aces and 23 winners, winning 86 percent of his first-serve points to knock out Canadian fourth seed Felix Auger-Aliassime 6-4 7-6 (7-5).
"The clay-court season wasn't the best for me, so I came here more motivated to start the grass season off well," said Fritz after reaching his first tour-level final since November. "I'm super happy that I've been able to start it off with a final.
"I'm locked in and ready to go. Once I start winning a couple of matches on grass and start feeling good, all the other things start clicking for me."
The second seed is eyeing a fourth grasscourt title, as he looks to continue to build momentum towards Wimbledon, where the 27-year-old is a twice quarter-finalist.
In the other European ATP event going on in Rosmalen, Ugo Humbert, the only seed left in the draw, crashed out to Gabriel Diallo 6-3 7-6 (7-4) in the semi-final.
The Canadian advances to a final duel with Belgium's Zizou Bergs, with the p[air both seeking their maiden title.
Bergs had little trouble overcoming Daniil Medvedev's American conqueror Reilly Opelka 6-1 6-4.
