The Cats led by 36 points early in the final term, but were forced to withstand a withering GWS comeback to prevail 13.16 (94) to 12.15 (87).
Fremantle's shock loss to St Kilda earlier in the day, coupled with a bye weekend for Hawthorn, allowed the Cats to leapfrog them both into second place, but only just.
The Giants kicked five of the last six goals to get within a kick with two minutes remaining, with No.1 NAB AFL Draft pick Tom Boyd kicking two of them to announce himself at the top level.
But Geelong had done just enough for a seventh consecutive win that takes it to 13-4 for the season.
The usual suspects of Joel Selwood (39 disposals), Steve Johnson (30 disposals, three goals), Harry Taylor (30 disposals) and Steven Motlop (28) were all pivotal in the victory, played out in front of just 7,697 fans on a chilly night in Sydney.
Co-captain Callan Ward (31 possessions), Adam Treloar (30 possessions, 10 clearances) and Toby Greene (32 possessions, nine clearances) were all immense for the Giants, who will have won plenty of admirers.
Both sides now enjoy a well-earned bye.
GWS defender Josh Hunt got the scoring underway against his old side, nailing a goal on the run in the second minute, before the Cats took control.
Dominating possession and keeping the ball pinned in their forward half for large periods, the only thing missing was goals, with five of their first six shots all resulting in behinds.
Jordan Murdoch's set shot gave the visitors some reward on the scoreboard, but Jon Patton's mark and goal after the siren made it just a one-point game at quarter-time.
GWS was well up for the fight, kicking the first three goals of the second term to suddenly break open a surprise 12-point lead.
That sparked the Cats into action as they registered the next six scoring shots, with a bit of Johnson magic from a tight angle giving them a four-point edge at half-time of an entertaining contest.
Geelong then slammed through the first four goals of the second half to break the game open for the first time.
But expectations of a landslide never eventuated, with the clock saving the Cats from a potentially damaging defeat.
GREATER WESTERN SYDNEY 2.4 4.6 7.9 12.15 (87)
GEELONG 2.5 4.10 10.14 13.16 (94)
GOALS
Greater Western Sydney: Patton 2, Boyd 2, Shiel 2, Palmer, Hunt, Kelly, Cameron, Hoskin-Elliott, Ward,
Geelong: Johnson 3, Hawkins 2, Caddy 2, Selwood, Murdoch, Duncan, Bartel, Guthrie, Simpson
BEST
Greater Western Sydney: Ward, Patton, Sheil, Hoskin-Elliott, Greene, Tomlinson
Geelong: Selwood, Caddy, Horlin-Smith, Johnson, Hawkins, Duncan
INJURIES
Greater Western Sydney: nil
Geelong: nil
SUBSTITUTES
Greater Western Sydney: Lachie Plowman replaced by Josh Kelly in the third quarter
Geelong Cats: Dawson Simpson replaced by Brad Hartman in the final quarter
Reports: nil
Umpires: Hay, Findlay, Mitchell
Official crowd: 7,697 at Spotless Stadium
