Cometh the hour, cometh the man. Arsenal needed their star player to be their match winner and he delivered early on in controversial circumstances.
He was the only one alive to the situation and despite the clear handball he carried on and finished well past Thibaut Courtois.
If this is his last game for Arsenal, he ended it doing what he does best.
Sanchez will be a huge asset to whichever club he decides to play for next season.
With Laurent Koscielny and Shkodran Mustafi missing, Arsene Wenger was forced to call upon his club captain, who hadn't started a match in 13 months.
But the experienced German did not let his under-fire manager down with an excellent display.
The subdued performance by the frustated Diego Costa was testament to Mertesacker.
Alexis Sanchez handball controversy for Arsenal against Chelsea Sat, May 27, 2017
Alexis Sanchez was involved in a hugely controversial moment during the FA Cup final
Play slideshow BT Sport 1 of 8 Danny Welbeck
The Arsenal striker has been incredibly unlucky with injuries throughout his career.
But Welbeck showed the huge impact he has on the team in a performance full of energy, pace and quality.
What might have been?
What if Arsenal had performed like this when it mattered in the spring?
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Their performance today will leave Arsene Wenger wondering why his team struggled so much.
It had the resilence, character and mental strength that he preaches about so often but rarely gets.
Behind N'Golo Kante, Chelsea's number 10 has been excellent and their stand-out player, but he had a difficult afternoon at Wembley.
He was unable to stamp his authority on the match in any way.
And he also suffered the embarassment of losing a challenge to Mesut Ozil.
Arsenal's Alexis Sanchez celebrates his goal against ChelseaVictor Moses
The right-wing-back has enjoyed a renaissance season under Antonio Conte.
But he was probably one of those whose place in the starting XI was most under threat.
And his costly red card won't have endeared him to Conte.
The Spain striker had a frustrating afternoon, well shackled by Mertesacker.
But after spurning a couple of chances he made no mistake once he finally got clear.
If this was his last performance in a Chelsea shirt, he will be sorely missed in English football.