Nadal, 29, will meet another Italian in Sunday's final, with 32nd-ranked Fabio Fognini beating French youngster Lucas Pouille 6-2, 7-6 (7/2) in the other last-four showdown.
Fognini, seeded eighth, is a familiar foe for the Spaniard, having already beaten Nadal twice this season in Rio de Janeiro and Barcelona.
For Nadal, it will be the 96th final of his career and his third in Hamburg, where he last won the title in 2008 by beating Roger Federer.
"I will try to keep playing well and enjoy today's victory," said Nadal, who has endured a tough 2015 in which he has lost his French Open title and slumped to his lowest ranking in a decade.
"These are important points for me -- 300 points for my goal of qualifying for the World Tour Finals is important. Matches like today help to bring you your confidence and your motivation for what you are doing."
Nadal, the world number 10, is now 25-6 on clay this season, and will on Sunday look to extend his streak of having won at least one European claycourt title every year since 2004.
"From the beginning I played great, since the first game that I hit a few winners," Nadal told www.atpworldtour.com.
"I was very comfortable on court today, feeling the ball well, with topspin to his backhand and then changing to his forehand down the line - a very important shot for me. In general it was a very positive match.
"Every victory is important. And this year with the up and downs that I've had, obviously every improvement is important. I played at a very high level.
"I'm very happy for that, playing with not many mistakes, very well with my backhand, very well with my forehand, hitting winners, changing speeds, changing directions. I think I played a great match."
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