Tim Cahill has brought success to Melbourne City at long last, scoring the only goal of the FFA Cup final against Sydney FC as the A-League upstarts claimed the first trophy in their seven-year history.

Cahill headed home Ivan Franjic's cross on 53 minutes to earn City the prize before hobbling off with a knee injury shortly after.

City will anxiously await a diagnosis on the star Socceroo, but whatever the outcome the club richly celebrated a maiden triumph.

Transformed by the millions provided by cashed-up owners City Football Group, the triumph showed the sleeping giants of Australian football have woken up.

City were right up for the AAMI Park decider, played between the A-League's top two sides in front of a record FFA Cup crowd of 18,751 on Wednesday night.

Coach John van 't Schip's ambitious attacking football came with a ruthless streak.

Within minutes of an impeccably-observed silence to honour the victims of the Colombian plane crash that killed an entire Brazilian football team, the battle was on.

City's Luke Brattan brought the fight, scything down Michael Zullo in front of an outraged Sydney bench.

Despite Milos Ninkovic shoving Fernando Brandan to the ground in a near 20-man melee, Brattan was the only man carded.

The heat remained after the brawl, with 10 fouls in the opening 15 minutes.

Sydney FC were getting into dangerous spaces but were unable to cut through.

Graham Arnold's side ended the half with 18 balls into City's penalty box, but only one shot — to the menacing Bobo.

City went forward less often but fluffed two chances to take the lead.

Cahill — recalled to the starting 11 as one of four changes — headed wide from fellow returnee Nicolas Colazo's free kick.

Bruno Fornaroli looked the man most likely to create something for City, and teed up Brandan only for the Argentinian to volley wide.

After the break, the 36-year-old struck.

Franjic's perfect delivery provided the platform, and Cahill rose in his indomitable style, freeing himself of marker Matt Jurman to head past Danny Vukovic.

He did not last much longer.

Cahill appeared to hyperextend his left knee under the weight of Josh Brillante's tackle from behind, lasting just a few more minutes before requiring a substitution.

The Sky Blues — playing without key defender Alex Wilkinson (virus) — chased the game and had their moments.

Bobo's header required a goal-line clearance from Michael Jaksobsen, while Osama Malik's injury-time tumble with Alex Brosque might have brought a late free kick.

It was not to be for Graham Arnold's side, which must wait at least six months longer to break their own seven-year trophy drought.

AAP