Characteristically solid in the air and sharp with ball in hand, Keenan shone at both ends of the field.
It was his crucial intervention that stopped Australia surging into a 31-12 lead before half-time when he hauled Joseph-Aukuso Suaalii down in front of the Irish tryline.
It wasn't the Leinster back's only defensive contribution, but it came at a critical time when the game was in danger of slipping away from the Irish, and laid the platform from which Jamison Gibson-Park scored Ireland's third try to leave just five points between the sides at the break.
Then, seven minutes after the restart, Keenan scored Ireland's fourth, elusively slipping between two Wallaby defenders after Garry Ringrose's offload.
In a see-saw game that went to the wire, the 30-year-old's contributions did not go unnoticed.
"Hugo Keenan was just so important, a proper game changer in that game," Ireland and Ulster centre James Hume said on the Ireland Rugby Social., external
"It was 33-31 and you had a guy who made three last-ditch tackles and a great try as well, a great line for that try under the sticks.
"You have players like that in your team who show up in big games like that and they can be the difference."