Collingwood's best-afield defender Harry O'Brien has been forced to deny using a homophobic slur against Geelong's Tom Hawkins in the Magpies' upset win on Saturday night.

Geelong suffered their first loss of the season, 15.12 (102) to 14.12 (96), after Collingwood (5-3) surged home with four goals to the Cats' one in the final term in front of more than 66,000 fans at the MCG.

Former All-Australian O'Brien was in sensational form with 31 disposals in defence and on the wing, while Hawkins finished with a game-high four goals and was crucial to Geelong's third-quarter fightback.

The Cats had trailed by 26 points at halftime but an eight-goal burst put Geelong in front by 13 points at the three-quarter change.

Collingwood claimed a morale-boosting victory with coach Nathan Buckley saying proudly it was a 22-man performance with no passengers.