Arsenal came from behind to beat Manchester City at Wembley and set up an FA Cup final clash with Chelsea.
Sergio Aguero had put City in front before Naco Monreal forced extra-time and Alexis Sanchez found a winner.
The result means Arsene Wenger will lead his team out in ninth FA Cup final on May 27th in what could be his final game in charge of the club.
The main action of the first half centred around referee Craig Pawson and all eyes were on the man in black as they went in level at the interval.
However, City should have been ahead going into the half-time break as replays showed the officials made a big mistake with a late call.
Leroy Sane’s cross found Aguero at the back post and the Argentine’s effort was kept out, only for Raheem Sterling to stab home the rebound.
But the whistle had already gone as Sane’s delivery was adjudged to have crossed the line for a goal-kick when only part of the ball was out of play.
It was harsh on the boys in blue. They kept plugging away though and were rewarded for their persistence on the hour mark.
A long ball over the top from Yaya Toure found Aguero in acres of space and the little striker showed composure to dink his finish past Petr Cech.
It was was a lead that lasted just 10 minutes though as the Gunners found a route back into the match.
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Alex Oxlade-Chamberlain’s whipped cross was met on the volley by Monreal and Claudio Bravo could do nothing to keep out the equaliser.
Manchester City had the better of the game in the second half and the woodwork twice came to the rescue of Wenger’s side.
Twice in two minutes in fact as Toure and Fernandinho both saw their names up in lights before lady luck decided to smile down on the Gunners.
With neither side able to find a way through, extra-time was needed to separate the two sides under the famous London arch.
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The momentum appeared to be with City despite conceding that leveller and Pep Guardiola seemed confident ahead of the additional 30 minutes.
But Arsenal have been victorious in their last six FA Cup matches that have gone to extra-time and they were not ready to end that sequence here.
Sanchez, who has long been linked with a transfer to City, showed them what they could be buying as he popped up with what proved to be the winner.
It wasn’t a pretty goal and he had barely even been in the game up to this point, however the Chilean found the crucial touch when it mattered.
His scrambled finish beat Bravo and sets up a London derby final date with Chelsea at the end of May.