A dominant Melbourne City rallied from a goal down to outplay 10-man reigning champions Sydney FC 3-1 and clinch their maiden A-League title Sunday.

In front of 15,000 fans at Melbourne's AAMI Park, the most allowed under coronavirus rules, they went to the break 2-1 up after strikes from Nathaniel Atkinson and Scott Jamieson cancelled out Kosta Barbarouses' opener for Sydney.

The tide really turned on 35 minutes when Sydney midfield anchor Luke Brattan was sent off after picking up a second yellow card, both for reckless challenges.

From there on Steve Corica's team were fighting a rearguard action and they did well to keep City at bay until Scott Galloway struck again three minutes into stoppage time.

"Credit to them, they've been the best club for the last few years and they kept coming," said City skipper Jamieson. "But that's amazing for us. I felt all week that we were good enough to do it."

It was sweet revenge for Melbourne who lost to Sydney 1-0 in last year's decider, denying Corica's side an unprecedented third straight title and sixth overall.

"City were just a bit too good tonight, so congratulations," said disappointed Sydney captain Alex Wilkinson.

Under new coach Patrick Kisnorbo, who used to play for Leicester City and Leeds United, City have shown discipline and physicality this year to finish the regular season top of the table ahead of second-placed Sydney.

They brought that dynamic into Sunday's final and were stronger and sharper, forcing three corners in the first five minutes.

But Sydney soaked up the pressure and stunned them by taking the lead, with Barbarouses picking up the ball just outside the box and unleashing a clinical strike that beat diving keeper Tom Glover on 21 minutes.

Less than three minutes later it was all-square again in a game played at a cracking pace.

Sydney failed to close down Stefan Colakovski on a counter attack and he found Atkinson, who took a touch and drilled the ball into the top corner.

Frenchman Florin Berenguer should have made it 2-1 for City soon after but wasted a free header, before a moment of madness saw Brattan sent packing.

He was already on a yellow card and saw red after a needless high lunge on Marco Tilio to leave his team fighting an uphill battle.

They paid the price just before half-time when Adrian Luna was brought down in the box and Jamieson cooly converted the penalty.

Sydney enjoyed some early possession in the second half, but City easily repelled them and they were unlucky not to go 3-1 in front on 60 minutes with a point-blank save from keeper Thomas Heward-Belle denying Colakovski.

A third goal seemed inevitable with City cruising but Heward-Belle repeatedly kept them in the game until Galloway's strike in the dying minutes.