Perhaps Dean Henderson needed a mask to disguise the mischievous grin on his face inside Old Trafford.

He must have been one of the few smiling from the sidelines though as David De Gea wasted no time in reminding us how fragile he has become in the Manchester United goal.

Five minutes to be precise.

That's how long it took him to make a stupid mistake after making a hash of a simple clearance from his own box and giving the ball straight to James McCarthy.

De Gea wasn't at fault when Palace took a shock lead two minutes later through Andros Townsend.

De Gea again won't be happy with his night's work with Manchester United

But soon after the suspect Spaniard was at it again, finding himself stranded miles from goal and in a tangle with Wilfried Zaha following some poor defending from Victor Lindelof.

It felt like the pantomime season had come early to Manchester - and watching it all unfold from the sidelines was Henderson, the man desperate to replace the man who seems to be doing his utmost to make it happen.

There appeared to be some redemption for De Gea deep into the second half when he kept out Jordan Ayew's penalty with a brilliant save.

But the feeling was brief after he was found to have left his line too soon and Zaha buried the second attempt, before beating De Gea again at his near post to seal a famous win.

De Gea was left unhappy with the penalty decisions
De Gea reacts after conceding the penalty from Zaha

The coming weeks and months promise to be a huge test of both keepers - for different reasons.

De Gea is 29 and still regarded as one of the finest in the business, but his crime sheet is getting longer at an alarming rate - even if the bells are not ringing inside Ole Gunnar Solskjaer's head.

The United boss has developed a blind spot when it comes to De Gea. He continues to show faith in him when it isn't justified and some people argue the Norwegian has become a soft touch.

Nothing highlighted this more than when Solskjaer replaced Sergio Romero with De Gea for United's FA Cup semi-final against Chelsea in July.

Henderson sat on the bench as De Gea started for United

The fact Romero had helped get United to the last four in the first place counted for zilch. Back came De Gea, who made two horrendous mistakes to gift Frank Lampard's men a 3-1 win and place in the final.

Solskjaer still thinks De Gea is 'the best keeper in the world'. Do me a favour. He isn't even the best keeper in Manchester.

The time has come for De Gea to stop making a fool out of his manager and show the strength of character needed to recapture the form and respect he once had.

In the meantime, Henderson, 23, will find his patience tested to the limit.

Henderson is as ambitious as they come. He wants to be England's No.1, let alone United's but if he thinks all it will take is a bad performance from his rival for his own chance to come, he can think again.

It looks like it is going to be a long season for De Gea again

Solskjaer appeared to base his selection for the visit of Palace on De Gea's recent performances for Spain when he said: "He played well for Spain in the summer and he's shown really good form in training.

"So has Dean to be fair, he played against Villa and didn't put a foot wrong. I'm privileged to have the goalkeeping department I have."

Perhaps the greatest privilege United have is that they now have someone in Henderson who appears capable of being the heir to De Gea's throne.

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United might have signed Donny van de Beek for £40m, but this feels like small change compared to the £900m club bosses have invested in new talent on a regular basis since 2013.

Yet considering the price of keepers these days and the fact United, unlike rivals Chelsea, Tottenham and Liverpool, continue to show respect towards the economic pressures on clubs caused by the impact of Covid-19, Henderson should go on to save them a fortune.

Provided Solskjaer recognises this fact and makes the most of what's right under his nose.