The Giants shook off a sluggish start in front of 34,824 fans to pick up right where they left off from last year's qualifying final win, surging to a fourth-straight win and relegating their fierce rivals to the unfamiliar ring of an 0-5 start to the season.

And once again the Swans didn't escape unscathed with Heath Grundy copping a nasty facial injury thanks to Jeremy Cameron crashing a marking pack in the third quarter. Grundy left the ground bleeding but returned sporting hefty cheekbone swelling and was thrown up forward.

Captain Josh Kennedy also didn't see out the game after a heavy head clash which left him bleeding profusely.

Whether he and Grundy join the likes of Dane Rampe, Sam Naismith and Jarrad McVeigh in the casualty ward remains to be seen.

The Giants also came out of the game wounded, with in-demand midfielder Josh Kelly leaving the ground in the last quarter with a left knee injury.

Four-goal hero Toby Greene could also be in strife next week after being reported for rough conduct in the opening quarter.

This was Sydney's third loss already this season at the SCG, and their sixth-straight dating back to last year's grand final defeat to the Western Bulldogs - unfamiliar territory for coach Longmire and the playing group.

"What we're dishing up at the moment's not good enough to be able to sustain the football that's required at AFL level for long enough," Longmire said.

"We're not able to do it at the present time. We need to start doing it pretty quickly.

"There's still a fair bit of footy to be played this year. We need to make sure we get back off the canvas and get going again,.

"There's no easy way to do it. There's a test in AFL footy every week. We haven't come up to scratch just yet, we need to come up to scratch pretty soon and we need to get going in a hurry."

Once again the Swans' wasted too much ball in their own half, with GWS kicking eight majors from turnovers.

But Longmire won't be pressing the panic button, with the fixture about to give the winless club a much-needed reprieve. Games against Carlton, Brisbane, North Melbourne and St Kilda beckon over the next month and there's enough time still to resurrect this ailing campaign.

"We're showing little bits and pieces here and there but the majority of the time we've not been able to sustain it," Longmire said.

"It's a combination of a lot of different things. It all adds up to that inconsistent performance and not being good enough for long enough."

GWS also has a potentially productive month ahead with games against St Kilda, Collingwood and Richmond to follow next Friday's preliminary final rematch against the Western Bulldogs.

The Giants have never been so far clear of Sydney on the AFL ladder, and Saturday's performance against the Swans was their fourth win over Sydney and their most dominant yet, equalling their record winning margin over Sydney.

Toby Greene's four goals means he now has 17 already for the season.

Ruckman Shane Mumford was enormous around the stoppages against his former club, dominating Swans duo Callum Sinclair and Kurt Tippett and winning the Brett Kirk Medal as best on ground.

Tom Scully and Zac Williams provided plenty of run through midfield, Callan Ward was his typical self in the engine room, forward Jeremy Cameron influenced all over the ground and Phil Davis did another solid job on Lance Franklin.

The Swans' star still finished with three goals, the last of which brought up his 800th in AFL football.

For a fleeting moment, it looked like this was going to be Sydney's night. Not even coach John Longmire would have dreamed of how well the Swans started the 12th Sydney derby.

They had four goals on the board within five minutes, and incredibly before the Giants had even managed to touch the football but they managed just five more for the game after that.

"We knew they'd come out breathing fire but to that level was a little bit unexpected," Giants coach Leon Cameron said.

"It's pleasing because it's a different way to win. Normally in the past maybe that could've turned out to be a six, seven goal quarter to the opposition.

"We kept on chipping away and everyone started to play their role and it was the reason we came into quarter time with the ascendancy back in our favour.

"The number one thing was clearly our defence.

"We were a bit shaky early this year but that was probably our best defensive effort collectively from all 22 that played. To keep the Swans to nine goals, clearly when they scored four in the first five or six minutes, was great."

All the stars combined for Sydney's first, slotted by Josh Kennedy after slick handball work from Isaac Heeney, Luke Parker and Dan Hannebery.

Tippett then marked strongly and went back to convert, before Tom Papley's flying shot from 40m out curled through.

The Swans forward marked strongly again moments later on the 50m arc before dishing it off to Franklin who sent through a booming left-footed finish to the delight of the astonished crowd.

But the Giants showed their growing maturity and didn't panic. Unbelievably, they led at the first break.

Cameron caused all sorts of problems for the Swans' defence which is badly missing Rampe, while Steve Johnson added to his endless highlight reel when he soccered through a volley to put his team in front.

The second quarter was even worse for the Swans who trimmed their forward line by throwing Sam Reid down back to try and stem the flow.

GWS managed four goals for the term, while the Swans could only muster three points.

Devon Smith kicked a pair, Greene grabbed his second and Callan Ward finished coolly from 40m to compound the Swans' misery. By now they'd kicked nine goals since Franklin hit the scoreboard in the first quarter.

This was a mature performance from the Giants. They controlled the flow of the game throughout and never let Sydney play the games on their terms, barring that remarkable opening five minutes.

The Swans were brave after the main break and kicked four goals to two, but any thoughts of a comeback were short lived and GWS ran away with it in the final term.

The gulf between Sydney's two teams seems to be widening in the Giants favour.