Canberra Olympic fell behind after 42 seconds, but responded brilliantly to beat arch-rivals Canberra FC 3-1 in the ACT National Premier League grand final at McKellar Park on Sunday.

Olympic midfielder Robbie Cattanch produced two pieces of free-kick magic to go with Daniel Colbertaldo's stunning strike to upset the league champions.

Cattanach was a worthy winner of the Valeri Medal as the best player in the grand final – Olympic's second victory in the decider in three years.

"We started off a little slow, they had a lot of chances early on, we just grinded out the result in the end and wore them down," Cattanach said.

"It's a big game, there's a lot of talk all week, and then you cop a goal against the champions after 42 seconds. You've just got to not panic, keep a level head and grind them down again."

Cattanach's masterclass capped a tremendous first season at Olympic after being named the best player in the ACT for the past two years at the Cooma Tigers.

Olympic coach Frank Cachia paid tribute to the impact Cattanach had made at the club.

"He's outstanding, there's no other way of saying it," Cachia said. "For someone with the CV he's got, he could swan around and do a lot more than he does, but he brings the young guys into the game and makes them feel welcome. He's all about putting the club and the team first."

Cattanach was one of a number of recruits to an Olympic side which needed a draw in the last game of the season to reach the finals.

They quickly built momentum with victories against Belconnen United and Tigers FC in successive weeks. But all of that confidence was shot when English striker Thomas James got on the end of a great ball from Domenic Giampaolo to open the scoring within the first minute for Canberra FC.

Olympic looked out of their depth, but Cattanach brought their supporters to life with a perfectly struck free kick low into the bottom corner to level the scores just before half-time.

His second, to put Olympic up 3-1 in the 68th minute, was just as classy, going high around the wall and exposing a gap left by Canberra 'keeper Sam Brown.

"I just had to make sure I didn't miss the target, there was plenty of space," Cattanach said. "Because I already had the first one under my belt, I think I was in his mind a little bit."

Colbertaldo chose the perfect moment for his first goal of the season, unleashing a wicked strike from 20m out to give Olympic the lead in the 64th minute.

It was Canberra FC's third straight grand final loss after going down 2-0 to Olympic in 2013 and to Belconnen United in a penalty shoot-out last year.

"It hurts a lot," Canberra FC captain Aidan Brunskill said. "To lose all three of them, it's not good enough for a club of our stature."

Canberra FC will have to regroup before they face Blacktown City in Sydney in the NPL quarter-finals next Sunday.

ACT NATIONAL PREMIER LEAGUE GRAND FINAL

Canberra Olympic 3 (Robbie Cattanach 45, 68, Daniel Colbertaldo 64) bt Canberra FC 1 (Thomas James 1) at McKellar Park on Sunday.