The Spanish teenager is targeting a fifth ATP title of the year, which would move him ahead of Rafael Nadal, having already triumphed in Rio, Miami, Barcelona and Madrid.
Alcaraz is set to move into the top five of the ATP rankings for the first time after seeing off Slovakia's Molcan 7-6 (7-2) 6-1 to reach yet another championship match on his debut in Hamburg.
The No.1 seed broke twice in the opening set but was pegged back on both occasions by Molcan, who was striving to reach a third final of 2022 after finishing as runner-up in Marrakech and Lyon.
But the 19-year-old dominated the tie-break, and found another gear to storm into the final as he made it eight successive sets won this week.
"It was tough," Alcaraz said. "Obviously, [Alex] played really well. The first set was really close; I'm really happy to be able to end the first set playing well.
"I couldn't read the drop shots from him. He was better on the drop shots today, so I was a little bit [frustrated] in the first set.
"In the second set, I think he was down a little bit; he didn't play well. I finished the match with a lot of confidence and played very well."
Standing between Alcaraz and another title is Musetti, who will appear in his maiden ATP final after he overcame Francisco Cerundolo 6-3 7-6 (7-3).
The Italian, who is set to climb into the world's top 50 for the first time, had lost six consecutive ATP Tour matches prior to this week.
But the 20-year-old continued his resurgence; ending the Bastad champion's eight-match winning streak by roaring back from 3-1 down in a second-set tie-break.
Meanwhile, Matteo Berrettini and Casper Ruud will target a third title of 2022 when they lock horns in the Swiss Open showpiece.
Berrettini – a winner in Stuttgart and Queen's before a positive COVID-19 test ruled him out of Wimbledon – registered his 12th successive victory, putting former US Open champion Dominic Thiem to the sword 6-1 6-4 in 78 minutes.
Reigning champion Ruud raced past Albert Ramos-Vinolas, winning five out of seven break points in a resounding 6-2 6-0 triumph.