The Swans navigated wet and windy conditions best to build a 19-point lead at the SCG before play was delayed at halftime because of nearby lightning strikes.
Play resumed at 10.02pm, with the Swans prevailing 17.5 (107) to 8.18 (66) after a brief Giants challenge in front of 43,986 fans on Friday night after a 7.50pm start.
The Giants' goalscoring output told the story, with spearhead Jesse Hogan (quad) a late scratching as the visitors failed to capitalise on 59 forward entries.
GWS were already without fellow forward star Aaron Cadman (concussion) and are left languishing in 14th place (2-4).
League leaders Sydney (5-1) wrestled back local bragging rights after last year's round-20 loss - the first time the Swans had suffered defeat after five-straight wins.
Swans defender Nick Blakey won the Kirk-Ward Medal for his best-on-ground performance, finishing with one goal from the centre square, 34 disposals and nine score involvements.
"The great thing about Nick is his development is about being a really strong two-way player and defending first and then attacking from that," Swans coach Dean Cox said.
"He's done that. He's clever enough now to put himself into positions where he can be dangerous on both sides of the ball.
"The run and carry is always a part of it, but it's the other aspects of his game he's really bought into which has been really pleasing."
Charlie Curnow kicked three goals, while Isaac Heeney had 28 touches and seven clearances after shaking off close attention from Giants youngster Ryan Angwin.
Clayton Oliver was easily the Giants' best at the contest, but his 37-disposal, nine-clearance effort wasn't enough to spark GWS.
Jake Riccardi stood tall in Hogan's absence with three goals, with Callum Brown called up after playing in the VFL immediately before.
Bursting from the blocks after the lengthy delay, Giants skipper Toby Greene notched three straight behinds, before Toby Bedford finally kicked truly to get the Giants humming.
But the challenge was short-lived, killed off by a Curnow goal.
Giants coach Adam Kingsley refused to get too downcast on the result, adding that Hogan is expected to return to action against North Melbourne next week.
"We hung in, we created shots," Kingsley said.
"Their ability to cope with our pressure was better than our ability to cope with their pressure ... but ultimately there's a lot to like about our game.
"I don't think we're too far away from being that team that we want to be, but we're not there yet."
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