Brighton proved to be Manchester United's kryptonite once again as the Red Devils fell to a late, late defeat at the Seagulls.
It was a game of plenty of chances but neither Luke Steele nor David de Gea were ever truly troubled for a sustained period. The Seagulls claimed all three points thanks to Alexis Mac Allister's injury-time penalty after Luke Shaw committed a handball from a Brighton corner, with VAR awarding a spot-kick.
United meanwhile are now two points behind Newcastle, though are secure in their top four spot despite their frustrating evening. Here, Mirror Football looks at five of the biggest talking points from Thursday's clash.
Martial walking tightrope
Over the course of pre-season, Erik ten Hag made it clear he rated Anthony Martial highly. After a series of injury issues, the Frenchman has finally been able to stay fit and is being handed regularly game-time.
But the attacker must be careful against getting complacent, with Ten Hag set to target at least one new forward in the summer window. The United boss was not afraid to show his frustration with the 27-year-old at Brighton.
He was seen slapping his thighs in anger before blasting Martial over a perceived lack of pressing. The forward later sent a tame shot so wide it ended up appearing to be a pass to Marcus Rashford, with Martial needing to step up his game if he wants a future.
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Mitoma impresses again
One of the stars of Brighton's impressive season has been Kaoru Mitoma and the 25-year-old starred once again against United. He gave Red Devils right-back Aaron Wan-Bissaka a challenging game, frequently getting involved in play.
The Japanese winger arguably should have done far better when finding himself one-on-one with David de Gea, and could have set up a team-mate for an easy tap-in. But it was still another impressive evening for Mitoma.
He appears set to become the next Brighton star to be desired by their Premier League rivals. And if his performances continue in this vein, the Seagulls will surely be able to demand a bumper fee.
Brighton continue to be kryptonite
It has now been five games since United defeated Brighton in a 90-minute match, having only been able to see off the Seagulls on penalties in their recent FA Cup semi-final. Brighton have won three of the past five meetings, drawing the other two.
And United continue to struggle to find a formula to overcome the South Coast side, having been left frustrated at the Amex Stadium on Thursday. In fact, Brighton enjoyed the majority of the possession as they continue to impress under Roberto De Zerbi.
United failed to find a way past Luke Steele in the Seagulls goal and paid the price thanks to Mac Allister's injury-time penalty. Ten Hag will need to go back to the drawing board next season if he is to finally secure a win over Brighton.
De Gea stakes claim for future
Less than a month remains of the Premier League season and David de Gea still has not signed a new contract with United. The Spanish keeper will see his current deal expire in the summer after more than a decade at Old Trafford.
Boss Ten Hag is expected to sign a new keeper in the summer, though it remains to be seen if they would come in as a back-up or a first-choice option. For his part, De Gea is doing what he can to convince United to hand him a new contract.
He stayed cool under pressure when dealing with errant backpasses from his defenders to show his improved distribution. But his shining moment was saving from Mitoma as he stood tall, with the ball hitting his face, before a late, late save from Alexis Mac Allister's long distance drive.
Casemiro's disciplinary concern
The trip to Brighton marked the 12th time Casemiro has been booked in all competitions this season. It is a concerning statistic to United boss Ten Hag, with the Brazilian having been one of his side's star players since his arrival from Real Madrid.
He has missed seven games in total through suspension, with the midfielder potentially needing to look at curbing his aggression next season. He was left walking a tightrope after his first-half booking against Brighton, far from ideal with United facing a team that were so fluent in attack.
