Hawthorn stared down the abyss of the worst AFL preliminary final upset of the modern game before staging a great escape to beat Adelaide by five points.
Late goals to Lance Franklin and Cyril Rioli and a crucial tackle by Ben Stratton saved the Hawks as they staved off an outstanding challenge from the Crows to win 13.19 (97) to 14.8 (92).
The Hawks will meet Sydney in next Saturday's grand final, the first time the two clubs have clashed for the premiership.
It will be the Hawks' first grand final since they upset Geelong for the 2008 premiership and Sydney's first since they lost an epic match to West Coast in 2006 by one point.
Hawthorn will start slight favourites, but they played below their best in Saturday's pulsating twilight final at the MCG.
Sydney also handed Hawthorn, the minor premiers, one of their worst losses of the season in round five and also led them by 38 points in the second term before the Hawks rallied to win their round-22 clash.
The overriding emotion for Hawks coach Alastair Clarkson after the match was relief.
"I was the only one having a baby in the last part of the game," he joked.
Hawthorn lost to Collingwood by three points in last year's preliminary final.
Clarkson added it would have been "horrendous" had the Hawks lost as a result of defender Ryan Schoenmakers giving up a crucial free kick during the final term.
The Hawks had gained a free kick because of Jason Porplyzia's crude spoil on David Hale, but it was reversed when Schoenmakers threw Porplyzia to the ground and the Adelaide player kicked a vital goal.
The Hawks easily won the inside 50s by 64-38 - at quarter-time it was 20-9 but they trailed by seven points.
That opening term set the scene for a grinding battle.
"There have been plenty of times in games like that where poor kicking actually costs you and we're lucky tonight that it didn't - we only just got across the line," Clarkson said.
"We only have one more crack at it, don't we, so we need to get it (conversion) right this week."
Hawthorn were five points down at halftime but kicked clear to lead by as much as 22 points in the third quarter.
The Crows refused to go away and after Porplyzia's goal, substitute Graham Johncock kicked another to put them a point ahead at 20 minutes.
But Rioli took a brilliant contested mark and goalled after the next centre bounce and two minutes later Stratton laid his game-saving tackle on Patrick Dangerfield in Adelaide's attack.
The Hawks rebounded and Franklin goalled to put them 10 ahead.
Taylor Walker kicked his fourth goal to reduce the margin to only five points, but there were less than 30 seconds left and the Hawks won the last centre clearance to ensure the win.
Kurt Tippett also kicked four goals for the Crows in what might be his last game for the club amid speculation he will soon join Brisbane or Gold Coast.
Crows coach Brenton Sanderson said his players were shattered but was full of praise for their performance.
"There's a lot of tears in the change rooms," he said.
"I'm so disappointed for them because they were so close to the ultimate game, but now we've had a taste of it I'm sure it'll burn and it'll hurt for a long time."
FACTBOX FOR 2012 AFL GRAND FINAL
Saturday, September 29
Hawthorn v Sydney at the MCG, 4.30pm (NZ time).
Head-to-head: Hawthorn 83 Sydney 66 Drawn 2
Last five meetings:
Rd 22, Aug 2012, SCG: Hawthorn 15.12 (102) bt Sydney 14.11 (95)
Rd 5, Apr 2012, Launceston: Sydney 16.10 (106) bt Hawthorn 10.9 (69)
Semi-final, Sep 2011, MCG: Hawthorn 19.8 (122) bt Sydney 13.8 (86)
Rd 9, May 2011, SCG: Hawthorn 15.16 (106) bt Sydney 8.12 (60)
Rd 19, Aug 2010 SCG: Sydney 19.15 (129) bt Hawthorn 13.7 (85)