Greater Western Sydney lost its co-captains before half-time and its star big man Jonathon Patton to a second serious knee injury of his short career, but scored a famous first-ever victory in Victoria over a woefully inept Melbourne on Sunday.

A pall fell over the lowest MCG crowd of the season as Patton lay face down on the wing two minutes into the second quarter, but the hush was replaced by jeers by the end of a game in which the muddling Demons had three goals to show for 345 possessions and 45 forward entries.

Exasperated a fortnight earlier after his team’s loss to Brisbane Lions, coach Paul Roos said it was a sub-AFL standard performance that left him embarrassed.

‘‘I’m embarrassed, the players can speak for themselves, but I mean you have to be,’’ Roos said. ‘‘Taking nothing away from the Giants, but they had three down. Whether guys are tired, throw the towel in, wave the white flag ...’’

Roos said it was fair to say his players looked like a group who wanted the season to finish. ‘‘I reckon you’re right, it’s a good assessment – today they let themselves down, they let the supporters down in particular, and I reckon they put the cue in the rack.’’

The Giants lost Phil Davis to concussion midway through the first quarter and his co-captain Callan Ward to a calf injury just before half-time. Only 19 players ran out after half-time, but a run of nine unanswered goals made a mockery of their manpower crisis. ‘‘They outran us, no question,’’ Roos said. ‘‘I think that tells you about their mentality compared to our mentality. They outran us and outworked us with 19 players. They [only] had 60-something interchanges. That tells you about where they’re at, which is a big tick for them.’’

After the three-quarter time siren sounded as the Demons fluffed another attack in the middle of the ground, Rhys Palmer sealed it with a dribbled major two minutes into the last before Colin Garland, swung forward with Lynden Dunn as James Frawley went back, kicked Melbourne’s first goal since the 24-minute mark of the first term.

Already missing prime movers Tom Scully, Lachie Whitfield, Jeremy Cameron and Stephen Coniglio, the Giants displayed a bravery their coach said you experience rarely in a career, overcoming a dire situation which he admitted left his coaching panel planning how to hold back the tide in five-minute blocks throughout the last half.

‘‘It’s a significant win – to win at the MCG, but to win the way we did with 19 fit men was phenomenal,’’ Cameron said. ‘‘We attacked and played really bold footy when we sensed the moment, and we held it up when we had to. There were times when we were thinking, ‘are we going to stop and are Melbourne going to come?’’’

The blight on an historic day came with the sight of Patton, his face a picture of woe, thumping his fist into the turf on the members’ wing. He limped off, unassisted but with head bowed, attempted some run-throughs along the boundary a few minutes later, but returned to the changerooms. He was taken to hospital for scans. The Giants later confirmed he had suffered a torn ACL. Cameron had been clinging to the hope that testing would not reveal the need for a second reconstruction.

‘‘You have this sinking feeling for the first 15 seconds. I actually didn’t know ... then all of a sudden you look and see him down there and he’s obviously under a fair bit of stress,’’ Cameron said.

‘‘Our thoughts go out to him and his family ... he’s had such a bad run with injuries, and this year he’s been so good for us. Cross fingers.’’

The 21-year-old ruptured the anterior cruciate ligament in his right knee in his 10th game last April, having missed the first half of 2012 after surgery in Sweden for patella tendonitis, a complaint that pre-dated his selection as the first pick of the 2011 draft.

He had been living up to his huge promise this season and entered Sunday’s clash having kicked 25 goals from 18 games.