In the teams' first meeting since Patrick Dangerfield put Hawthorn to the sword in last year's preliminary final, the Hawks trailed by six points when Geelong's Shannon Neale kicked his fourth goal with less than two minutes remaining.
Mitch Lewis levelled the scores with 51 seconds to go then evergreen Jack Gunston cannoned the winning point into the goal post with 13 seconds left to deliver a 13.14 (92) to 14.7 (91) victory in front of 84,712 fans at the MCG.
Mitchell said he and his assistant coaches couldn't hear each other on the bench late on and the comeback, which snapped Geelong's five-game winning streak over Hawthorn, was entirely down to the players.
"Our players this time get to write their names into the history of what's a great rivalry," Mitchell said.
"For the next 10 years you'll show the last couple of minutes of that game. And all of our new players, who perhaps haven't done that against the Cats, they get to be a part of it for the first time.
"I was really proud of the lads that we could get over them today."
Skipper James Sicily played through a right shoulder injury and took a huge contested mark in defence before kick-starting an end-to-end play that finished with Gunston scrapping the winning point.
The 34-year-old Gunston played through a right hamstring scare while debutants Flynn Perez and Jack Dalton were each left bleeding from the face from high knocks.
"I'm not usually big on the sort of war analogy, but it felt like that," Mitchell said.
"That was a game where you needed to lean on everything.
"When you win a game by a point, a lot has to go right, and all of the resilience of every player, of every staff member goes into winning it."
The game was played on a knife's edge, with multiple lead changes.
Geelong led by a game-high 13 in the fourth and appeared set for victory before a miraculous Nick Watson snap from a pocket inspired a Hawthorn surge.
Both teams fluffed chances to bury the game, and Mitchell joked Hawthorn "found unique ways to not score", before the hectic finish.
Mitchell was confident Sicily had just suffered a "stinger" and said hopeful Gunston had only experienced cramp ahead of Saturday's Gather Round blockbuster with the unbeaten Western Bulldogs at Adelaide Oval.
Gunston worked over Jack Henry and kicked 3.4 while Watson kicked three superb goals and Jack Ginnivan (two goals) was lively.
Josh Ward (29 disposals) was busy, especially in the first half while Connor Macdonald (26) was excellent when it counted.
For Geelong, who were missing Dangerfield (calf), Bailey Smith (33 disposals) worked tirelessly with support from Max Holmes (27 disposals) and Tanner Bruhn (26) while Tom Stewart was busy.
Hawthorn flew out of the blocks in Mitchell's 100th match as coach but Geelong turned the game into an arm wrestle.
Hawthorn always looked capable of a surge and delivered one for the ages.
"In the end I didn't think we played well all game," coach Chris Scott said.
"I'm never happy to lose. But I thought they probably had their chances to win it late and we almost stole it.
"In the end, with the score the way it was, it sort of looked like it was the other way around."
Geelong face West Coast at Norwood Oval on Sunday.
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