Jim Gavin had to turn to one of his forgotten men to secure back-to-back All-Ireland titles
2014 was meant to be the start of the next great Dublin career.
20-year-old Cormac Costello had excelled in limited cameos for Dublin throughout the championship, using his searing pace to trouble defences and kick a series of impressive scores.
Dublin were going for a two in-a-row, and as they took the field against Donegal in the All-Ireland semi-final, they had yet to lose a game of note under Jim Gavin.
As always, there were selection dilemmas in the build-up, and there was a surprise when the teams lined up for the pre-match parade.
Cormac Costello, only two years out of minor, was starting Dublin's biggest game of the season - and deservedly so.
Unfortunately, Costello - like so many established stars - struggled in the face of one of the all-time great team displays from Donegal.
The young attacker fluffed a goal chance early on that could have put Dublin out of sight and he was hauled off five minutes into the second half.
Martin Breheny's report in the Irish Independent at the time rated him as a 5 out of 10 - it was a tough learning experience for Costello.
Costello fell out of favour thereafter, struggling with injury and form to the extent that he was an almost non-existent presence as Dublin bounced back from their Donegal defeat by winning the All-Ireland title in 2015.
This year was not as straightforward. Dublin may have lifted the Sam Maguire today, outlasting Mayo by 1-15 to 1-14, but they did so despite poor seasons from established stars like Bernard Brogan and Paul Flynn, while the scores also dried up for Diarmuid Connolly and Ciaran Kilkenny during their two match battle with the westerners.
Midway through the second half, Gavin trusted that Costello had learned the lessons of 2014.
He exploded off the bench and kicked two key scores almost immediately. He was direct and clinical - something that couldn't be said of Dublin's starting forwards bar Kevin McManamon.
Then when Mayo roared back into the game, Costello put Dublin two up with another crucial score.
It is a testament to Dublin's strength in depth that a player hovering on the periphery was able to step up in such a crucial moment and swing the balance of play.
"We have such a strong panel that I was just waiting for my chance," Costello told RTE afterwards.
After two years out of sight and out of mind, the youngster reminded everyone why he was so highly rated in the first place.