German Kohlschreiber lost the first set against his Italian opponent but bounced back to take the win 6-7 (6/8) 6-2 6-2.
That victory ensures Kohlschreiber, who reached the quarter-finals at Wimbledon earlier this summer, will be break into the top 20 of the world rankings for the first time when they are released on Monday.
"I knew that at some point this year I could reach the top 20. It's great that it will happen now, when I play for the trophy," said Kohlschreiber on www.atpworldtour.com.
Facing the 28-year-old Kohlschreiber in the final will be third seed Robin Haase, the defending champion.
The Dutchman beat fifth-seeded Slovakian Martin Klizan 6-3 6-3 in the second semi-final.