The reigning premiers downed this season's premiership favourites 18.10 (118) to 17.14 (116) in front of 65,287 fans at the MCG, their ninth straight win over the Hawks and possibly their most stunning yet.
The Hawks will be seeing blue and white hoops in their nightmares after they reeled in a 51-point deficit to gain an eight-point lead deep in the final term, only to be overtaken by two late goals to best afield Hawkins.
His last was his best, booted from outside 50m, after Geelong had taken the ball the length of the field in the final seconds.
Hawthorn had entered the match on an eight-game winning streak, all by big margins and as the competition's form team, but this latest loss to the Cats is sure to leave mental scars if they meet again in the finals.
Geelong's win was their third in succession, all against top-eight sides, Essendon, Adelaide and the Hawks, as their late-season claim to be considered among the top flag contenders grows more impressive by the week.
The Cats' start was stunning, kicking the first 5.2 of the match and 9.3 to 2.0 for the first term to open a 45-point lead by the first change.
With captain Joel Selwood leading the way in the midfield, Paul Chapman had three goals by quarter-time and Steve Johnson two, while Hawkins added his second soon after the break to stretch the gap to 51 points.
But the Hawks, who had allowed the Cats to move the ball too freely in the first term, sprang to life with a vengeance.
Having laid just six tackles in the first quarter, they produced 26 in the second and desperate defensive acts all over the field to work their way back into the match.
Despite some simple missed shots for goal, they were back within 17 points at the main break.
Sam Mitchell and Brad Sewell did plenty of midfield grunt work, Luke Breust and Cyril Rioli providing spark in attack while Jack Gunston kicked four majors.
The Cats were still 19 points clear at the last change and again 10 minutes into the last term when Hawkins kicked his fourth.
But the Hawks fought desperately, with a Rioli snap and cool set shots to Gunston and Brendan Whitecross levelling the scores.
Sewell then gave his side the lead for the first time almost 25 minutes into the term with a great snap from a forward line contest.
But missed shots by Breust and David Hale kept the Cats in touch, allowing Hawkins to produce a brilliant snap before capping the win with his last-gasp heroics.
Cats coach Chris Scott said his side had shown that their best remains very good and they were finding it at the right time of the year.
"We've suggested for most of the season that we think we can get better and we planned to play our best footy at the end of the season," Scott said.
Hawks coach Alastair Clarkson said his side could take some heart from reeling in such a big deficit, despite the obvious pain of defeat.
"I was pleased with the resilience of the group that we fought back and got ourselves back into the contest and from that position we probably should have won the game," he said.
Hawks midfielder Liam Shiels will attract scrutiny for an elbow to the head of Allen Christensen off the ball in the third term.