United were 3-2 up and seemingly home and dry when Noni Madueke was felled by Diogo Dalot in the seventh minute of added time. Palmer scored from the penalty spot to seemingly rescue a point - but a stunning finale awaited.

The former Manchester City player - a United fan as a youngster - was given space inside the box and lashed it beyond Andre Onana with virtually the final kick, with the aid of a slight deflection off United's Scott McTominay.

Their side had looked like running away with the Premier League contest in the first period, Conor Gallagher and Palmer from the penalty spot putting them into a 2-0 lead inside 20 minutes.

But a horrendous error from Moises Caicedo gifted United a way back, Alejandro Garnacho netting his first before Bruno Fernandes nodded unmarked past Djordje Petrovic to level before the break.

A breathless second half could have seen either side win it, and Garnacho looked to have done it for United when he headed in a brilliant cross from Antony midway through the half.

Then came scarcely believable drama at the end, with Palmer's double sparking joyous scenes among home supporters.

Chelsea had looked irresistible for much of the first half and raced into a deserved lead.

First, Enzo Fernandez scooped a delicious ball into the right channel for the overlapping Malo Gusto. His low cutback pinged off the heel of Raphael Varane, spinning favourably into the path of Gallagher whose first-time drive slithered beneath Onana's outstretched hand and into the net.

The second goal came from a similarly neat move down the other flank, this time Marc Cucurella feeding Mykhailo Mudryk who bolted onto it and flicked the ball back inside to Cucurella. Across to challenge came Antony, felling the Chelsea defender with an artless trip. Palmer dinked his penalty into the bottom corner with consummate ease.

United struggled with the pace and directness of Chelsea's transitions but the hosts' control of the game was punctured on 34 minutes.

Caicedo sensed Antony lurking on his shoulder and played a hurried, careless ball square that sold Benoit Badiashile short. Garnacho was onto it like a flash, tearing clear of the hapless Chelsea pair and slotting past Petrovic.

Onana pushed out Fernandez's low hit and had to be bailed out by Aaron Wan-Bissaka, who shovelled the rebound away from Mykhailo Mudryk as Chelsea quickly resumed their assault.

But the goal had swung the game towards United and they were soon level. Antony swept the ball wide to Garnacho, who stood up Cucurella and knocked it back for Diogo Dalot. His cross whizzed across the box to Fernandes, arriving unmarked at the far post, to wipe out Chelsea's lead.

Gallagher rattled the post when set up by Palmer late in the half, though they were clearly stunned by United's rapid double and looked grateful to go in level at the break.

The second half was a gung-ho battle between defence and attack. At times, the midfield simply vanished as both sides ripped into each other, and by the hour mark either could have led, Fernandes and Palmer with the clearest chances lashed over as the game hummed with energy, coaxing a winner.

It looked to have arrived from Garnacho. Antony's cross, whipped with the outside of his left boot, was elegant and pinpoint. Chelsea had two defenders back but neither tracked the run of Garnacho, who stooped bravely to reach the ball before Petrovic and guide it into the corner. The United fans, including new Kansas City Chiefs recruit Louis Rees-Zammit, were delighted.

It looked like staying that way until the final minute of stoppage time, when Palmer's dramatic double sealed an astonishing turnaround.

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