London - Manchester United moved to within three points of fourth-placed Chelsea with a smash and grab 2-0 win at Stamford Bridge thanks to goals from Anthony Martial and Harry Maguire on Monday.
Chelsea had two goals disallowed by VAR reviews and were furious Maguire was not sent-off early on for an off-the-ball kick out at Michy Batshuayi.
However, Blues boss Frank Lampard cut a frustrated figure as the flaws in both boxes which have seen his side win just four of their last 14 league games were exposed once more against ordinary opposition.
Victory lifts United up to seventh and within two points of Tottenham in fifth, which could be good enough to qualify for the Champions League next season pending Manchester City's appeal again a two-season ban from European competition.
Lampard made a bold call before kick-off by again dropping the most expensive goalkeeper in football history, Kepa Arrizabalaga, to the bench in favour of the 38-year-old Willy Caballero.
Batshuayi also started with Tammy Abraham ruled out by injury and Lampard's anger at missing out on a striker in the January window was borne out by a poor night for the misfiring Belgium forward.
Chelsea suffered another injury blow early on when N'Golo Kante hobbled off and the France World Cup winner is now a doubt to face Bayern Munich in the Champions League next week.
The loss of Kante did not disrupt the home side's early rhythm as Reece James and Willian fired just wide.
Chelsea were then furious Maguire somehow escaped without being sent-off for kicking Batshuayi after the two collided in front of the dugouts.
The former Marseille attacker then squandered the first of a host of chances by firing wide from Mason Mount's cut-back.
Chelsea's sense of injustice increased when Willian was harshly booked for diving as he went down under a challenge from Bruno Fernandes looking for a penalty.
United had not made Caballero make a single save before going in front a minute before the break when Martial planted a brilliant header into the far corner from Aaron Wan-Bissaka's cross.
There was still time for Batshuayi to miss another chance before half-time when he skewed wide from a narrow angle.
The one-way traffic continued at the start of the second period as Mount hit the post and a brave block from Wan-Bissaka deflected Pedro's goal-bound effort behind.
But even when Chelsea did get the ball in the net through substitute Kurt Zouma, the goal was ruled out by VAR for a push on Brandon Williams by Cesar Azpilicueta.
Fernandes was unable to make much of an impact from open play in his second United appearance since a £47 million move from Sporting Lisbon.
However, the Portuguese international is a huge threat from set-pieces and nearly caught Caballero out with a free-kick that crashed back off the post.
Moments later, Fernandes provided his first assist for the Red Devils with a corner which Maguire powered home.
Lampard had seen enough from Batshuayi and handed Olivier Giroud a rare appearance off the bench for the final quarter.
The French striker thought he had given Chelsea a lifeline with a near post header, but was ruled offside after a VAR review.