Nicholls, who admits he enjoys the Monmore track, top scored in qualifying after five impressive rides using the unique handicap format with 13 points.
He finished three points clear of home skipper Rory Schlein and just got the better of him in the final.
All four finalists – Nick Morris and Peterborough man Chris Harris were the others – were level going into the third turn of the first lap and Schlein looked good, but Nicholls made a smart move to be the leader coming out of turn four.
Harris notched nine points from his qualifying rides to make the final.
Nicholls said: “This is a real fun meeting and it’s great for me to win it. I always enjoy racing in it so I was delighted to be in it and the racing is always enjoyable on a good track like this.
“It’s great to round the season off with another honour on the board!”
SCORERS (after 15 qualifying heats): Scott Nicholls 13, Rory Schlein 10, Chris Harris 9, Nick Morris 9, Luke Becker 8, Ryan Douglas 8, Sam Masters 8, Norick Blodorn 7, Broc Nicol 6, Ricky Wells 6, Ty Proctor 3, Leon Flint 3.
GRAND FINAL: Nicholls, Morris, Schlein, Harris.