Hull stunned the Gunners at a sun-baked Wembley as they went 2-0 up inside eight minutes through James Chester and captain Curtis Davies, who both capitalised on some poor defending from balls into the penalty area.
After several Arsenal penalty claims, notably a pull by Tom Huddlestone on Olivier Giroud, were turned down by referee Lee Probert, the equaliser eventually came on 71 minutes when Laurent Koscielny knocked the ball into the net from a corner before being clattered by Allan McGregor.
The Hull goalkeeper saved well from Giroud as the match went into extra-time when the France forward Giroud crashed a header against the crossbar.
However, it was left to Aaron Ramsey - who left Wembley in tears as a schoolboy following defeat with Cardiff in the 2008 final against Portsmouth - to complete a remarkable turnaround when he crashed in a loose ball from the edge of the penalty box on 109 minutes which handed Arsene Wenger his first taste of success since 2005, and might just convince him to sign a new contract.
Gunners boss Arsene Wenger told ITV: "We wanted to make history tonight and win the game, and we made history in both ways - how not to start a cup final and how to come back.
"I'm very happy for the players because I think it was a turning point in the lifetime of this team, and to know they can win in that way was very important today."
Wenger admitted it would have been "terrible" had they not been able to fight back, but said: "We came back. I've praised many times the spirit of this team and I'm very proud of that today.
"Congratulations to Hull, they played fantastic for the whole game. We won it in the end but they played very well."
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