That lead held up until well into the second half, and Chelsea's situation became even more dire after Nigerian winger Victor Moses was sent off in the 68th minute for diving.
But Diego Costa sensationally levelled for the 10 men on 77 minutes, only for Aaron Ramsey to hit an instant reply for the Gunners just 60 seconds later after a cross from substitute Olivier Giroud. "I've said before that this team will win the championship with one or two buys".More news: Tillerson: Trump put 'pressure' on Netanyahu and Abbas to revive negotiations
"We had an outstanding performance from the first minute onwards". Honestly, the goal after three minutes in this way, it [should have been] disallowed because there was a clear handball but our start wasn't good for the first 20-25 minutes then we started to play. They've united and responded.
The flag was initially raised on the far side for a possible offside against Ramsey who was stood alongside Sanchez.
However, after conferring with his assistant, referee Anthony Taylor elected to allow the goal to give Arsenal a surprising early lead in the cup final.
Already booked for holding back Welbeck on the touchline, Moses was shown a second yellow card for hurling himself to the ground in the Arsenal box in anticipation of an Alex Oxlade-Chamberlain challenge that never came.More news: Manchester bomber 'part of terror network'
Players of both sides were to wear the armbands as a tribute to the victims of the Manchester bombing last week but it appears someone in the Chelsea dressing room forgot to hand them out.
Chelsea struggled immensely to cope with Arsenal's intensity and impose themselves, with the Gunners arguably producing their best 45 minutes of the season.
Ramsey, the match-winner in 2014 against Hull, ran through to head home as Antonio Conte's men went close to a famous double, without a celebratory cigar.
David Ospina denied Costa with a save off his face before Cahill was forced to clear off the line for the second time, as from the counter attack, Hector Bellerin fed Welbeck, who saw his deflected shot beat the Chelsea goalkeeper but not Cahill.More news: Syria, Russia slam U.S.-led attack on pro-Assad forces
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