Alexis Sanchez delivered one of his finest performances for Manchester United on Friday night.Returning to his former club Arsenal, the Chilean brushed off his difficult form this season for a blockbuster FA Cup fourth round tie, which the Red Devils eventually won 3-1.Sanchez scored the opening goal - only his fifth since moving to Old Trafford - by rounding Petr Cech and finding the net he so often rippled during his time in north London.Further goals from Jesse Lingard and Anthony Martial would cancel out a Pierre-Emerick Aubameyang strike and ensure United progressed to the next round.It also, of course, elongated Ole Gunnar Solskjaer's remarkable 100% record since replacing Jose Mourinho back in December.

Arsenal 1-3 Man Utd

Sanchez has struggled for game-time in spite of the managerial switch, but will be hoping his performance against Arsenal will start to change things.

And there's definitely evidence to suggest that the 30-year-old is in better spirits and if United fans are to be believed, that's summed up by his recent Instagram activity.

It's no secret that Sanchez loves his two dogs Atom and Humber, even going as far as creating an Instagram account for them with over 180,000 followers.

Instagram story mocking Arsenal

Sanchez definitely plays a key role in updating the account, which is often graced with dramatic compilations of Atom and Humber set to emotional music.

That certainly wasn't the case on Saturday, however, as a post appearing to poke fun at Arsenal was uploaded to the account's Instagram story.

It shows Sanchez superimposed on to a movie poster with the title 'I Am Back' as well as an amusing subtitle of: 'He came back to play the piano. They faced the music.'

It's fair to say United fans are convinced it came from the man himself. Check out the post and the reaction below:  

Come on Alexis, was it you?

There's nothing untoward about the post but it's certainly cheeky, especially when you consider Sanchez made over 150 appearances for the Gunners.

Either that or somebody in Sanchez's family or team just couldn't resist sharing the post.

Regardless of Instagram activity, though, Sanchez will be feeling good about finding the net for United and will turn his focus to becoming a regular starter on Solskjaer.

If he can produce the kind of showings that silenced Arsenal on Friday night, then there's every reason to suggest he could compete with Martial and Marcus Rashford.

Supporters know he can succeed in the Premier League and his previous form at the Emirates shows that but Sanchez is still a long way from returning to his best.

He'll have to hope that - like the poster says - he really is back.

Do you think Sanchez should start for United? Have your say in the comments section below.