Martins pounced in the 90th minute after a dreadful mix-up between Arsenal goalkeeper Wojciech Szczesny and defender Laurent Koscielny gifted a chance to the Blues' Nigerian striker.

The last-gasp winner was no less than Birmingham - whose owner Carson Yeung was celebrating his 51st birthday - deserved after a gutsy performance at Wembley that saw them make a nonsense of Arsenal's pre-match status as heavy football favourites.

But it was a disastrous result for Arsenal, who had been desperate to lift some silverware this year for the first time since their 2005 FA Cup final win over Manchester United.

Birmingham manager Alex McLeish - who had enjoyed huge success north of the border with Rangers winning seven trophies - said that it was a remarkable result given several of his players hadn't been able to train all week and others were running on empty at the end.

"This feels like the best ever win of my life," said 52-year-old McLeish.

"In relative terms for us to put one over Arsenal is a titanic result."

Birmingham - for whom it was only the second ever major trophy in their history with the previous one the 1963 League Cup - had taken the lead in the 28th minute, when a rare foray into Arsenal territory resulted in a corner met by defender Roger Johnson.

The centre-half's header found striker Nikola Zigic on the edge of the six-yard box and the tall Serbian striker easily outjumped his marker to guide a back-header into the Arsenal net.

Arsenal might have equalised immediately when a Bacary Sagna cross from the right flank was met by Robin van Persie, but the Dutchman's diving header flew just wide of the top corner.

Zigic should have put Birmingham two goals up when he again found himself clear on goal, only for Szczesny to pull off a point-blank block with his legs.

And on 39 minutes Birmingham were made to pay for their profligacy when Arsenal grabbed an equaliser.

A thunderous shot from the edge of the area by Jack Wilshere cannoned back off the crossbar, and when Birmingham failed to clear, Andrey Arshavin jinked down the right flank and whipped in a low cross for van Persie, who twisted his body into position superbly to volley home.

Until the exchange of goals, the biggest talking point had arrived after only two minutes when Birmingham were denied a penalty which should also have seen Szczesny sent off.

A deft pass from Zigic sent Lee Bowyer racing through on goal and the midfielder rounded Szczesny only to be brought crashing down by the keeper.

But instead of a red card and a spot-kick, Arsenal were given a huge let off when Bowyer was ruled offside. Replays subsequently showed Sagna had been playing Bowyer yards onside.

Arsenal began the second half brightly, and carved out an early chance when Sagna's low cross was met by Tomas Rosicky, only for the Czech international to sweep his shot just wide.

Birmingham refused to be cowed however, and the introduction of Jean Beausejour for Craig Gardner gave their attack a fresh outlet.

Beausejour was involved in the build-up on 57 minutes when Keith Fahey lashed a shot against the foot of the post with Szczesny well beaten.

With extra-time looming, Arsenal stepped up the pace and tested Foster twice in quick succession.

First Nasri forced a fine save out of the England international and then Nicklas Bendtner, who had come on for van Persie, rifled a low shot that the Birmingham keeper did well to smother.

Foster was again pressed into action on 80 minutes, Nasri once more whipping in a curling shot from near the edge of the away that was beaten away.

But just as Arsenal turned the screw, Birmingham struck the killer blow. A long goalkick by Foster was met by Zigic and when Koscielny and Szczesny bungled the clearance, Martins was on hand to jab home.

Where does this upset rate? What do Arsenal have to do to finally win a trophy?