GWS have pipped Richmond by two points at Spotless Stadium, showcasing their AFL premiership credentials while extending the reigning premiers' miserable record outside Victoria.
The Giants stormed back into the top eight on Saturday night, resisting a final-quarter fightback to triumph 11.13 (79) to 10.17 (77).
Richmond youngster Shai Bolton put his set shot out on the full with two minutes left in a thrilling rematch of last year's MCG preliminary final.
Veteran forward Jack Riewoldt then gave his side hope of snatching victory, snapping truly to trim the hosts' lead to a point with 26 seconds remaining.
The Tigers couldn't win the all-important final clearance, with Dylan Shiel showing great composure when it mattered most.
Toby Greene, playing his first game after spending almost three months on the sidelines because of a foot injury, kicked GWS's only goal of the final quarter.
It was a clutch effort from deep in the pocket.
"We want to play finals and go deep in finals, so this is a good stepping stone," Greene told Channel Seven.
The upset, inspired by superb games from GWS stars Stephen Coniglio, Heath Shaw, Callan Ward and Lachie Whitfield, could also have major ramifications in the race for the minor premiership.
The winner of Sunday's contest between Collingwood and West Coast will equal the ladder-leading Tigers on 48 premiership points, as will Port Adelaide if they defeat Fremantle.
Based on Richmond's away record this season, the flag favourites will be keen to secure a home qualifying final as they seek to go back to back.
All four of the Tigers' losses this season have now come away from Melbourne, although they were far from disgraced at Spotless - booting four of the game's final five goals.
The visitors had a severe case of the yips but none more so than Jason Castagna, who finished with five behinds and put another set shot out on the full.
"He'll probably be a little bit distraught about his 0.5 but I thought his game was terrific," Richmond coach Damien Hardwick said.
"The finishing wasn't there but it'll be there next week.
"We did some things really well tonight ... but we just couldn't seem to capitalise on our dominant patches like they did."
Richmond lacked their trademark polish most of the night, especially in front of goals, but rallied when GWS opened up a 21-point in the first quarter then a 24-point buffer in the third term.
""We knew they'd come in the last quarter, they have a great last-quarter record and we were coming back from Perth on a six-day break," Giants coach Leon Cameron said.
"It was a cracking game."
GWS, whose campaign was on the cusp of full-blown crisis in May after a month-long losing streak, next face Port Adelaide at Adelaide Oval.