On Friday Grassl's short program left him in fifth place after he fell on a quad flip and hung on to a triple Lutz in the first of his two brand new programs.
A score of 74.26 left the home favourite in fifth place as Azerbaijan's Vladimir Litventsev topped the men's short with 80.83 points, France's Adam Siao Him Fa a fraction behind him on 80.54 points.
But Sunday's free skate was a different story as Grassl landed three quadruple jumps to score 173.54 giving him an overall score of 247.80 points, and victory 10 points ahead of Siao Him Fa.
The French skater finished in second place on 237.36 while Georgian skater Morisi Kvitelashvili (236.18) was third and Litventsev finished just off the podium in fourth.
"I’m very happy for this win after I changed both my programs," Grassl said to Italian broadcaster RAI, "my next events will be in Las Vegas and then the senior Grand Prix in Turin (4-7 Nov)."
Skating to 'Interstellar' and 'Armageddon', Grassl put on a show in Bergamo on Sunday landing a quad Lutz, a quad flip, a quad loop, two combinations which included four triples, and a final triple Lutz to seal it.
Still mastering his new programs, when he gets them down this could be a big season for the reigning three-time Italian national champion who always aims high.
Lombardia Trophy men's singles results: Top 10
1. Daniel Grassl 247.80
2. Adam Siao Him Fa 237.36
3. Morisi Kvitelashvili 236.18
4. Vladimir Litvintsev 218.80
5. Tomoki Hiwatashi 213.11
6. Romain Ponsart 204.39
7. Arlet Levandi 198.67
8. Aleksandr Selevko 197.71
9. Davide Lewton Brain 193.02
10. Konstantin Milyukov 192.41