With his late winner, Scott McTominay now has seven Premier League goals to his name this season, the most of any player for Manchester United.
Four of those seven have come when introducted as a substitute, the joint-most by any player in the division in 2023-24 along with Brighton's Joao Pedro.
Erik ten Hag had United fans scratching their heads when he replaced Marcus Rashford with Scott McTominay with 17 minutes remaining.
But any thoughts that it was a defensive move were swept away as the Scottish super-sub struck United's winner four minutes from the end of an epic 90 minutes.
Kobbie Mainoo set up Diego Dalot wide on the right and the full-back swept in a stunning cross which McTominay pounced on to head powerfully beyond Emi Martinez.
It was the Scot's latest smash and grab act and it pulled United to within five points of Villa with their fourth win on the spin in all competitions.
Villa will feel robbed as they dominated play after the break but Ten Hag's switch paid off spectacularly.
Aston Villa's 23 shots were the most in a single Premier League game this season, but they could only convert one when Douglas Luiz diverted in Leon Bailey's cross.
The final whistle goes - and the gap between Aston Villa in fifth and Manchester United in sixth is down to five points.
It still sounds a tall order for the Red Devils, but it was five minutes away from being eight points and could have easily been 11.
Scott McTominay was the hero, off the bench again to plunder a late winner.
90+5. One last push for Villa as United drop all 11 men behind the ball.
Tielemans can't find room for the shot so Carlos takes over and loops a cross...
...straight at Onana, who drops to the turf with the ball in his hands.
United are almost there.
90+3. Garnacho almost seals it on the break but, not for the first time today, an important toe-in by Carlos helps the ball into the hands of Martinez.
90. Manchester United will have six minutes to see out if they are to register a big win. What do Villa have left?
88. As soon as the ball struck the back of the Villa net, Unai Emery moved to make some final changes.
He's thrown Nicolo Zaniolo and Lucas Digne for the final minutes with John McGinn and Alex Moreno making way.
86. Scott McTominay doing Scott McTominay things!
The much-maligned midfielder has once again come off the bench in a move questioned by many, and popped up with a late goal that could prove vital in the race for Champions League football.
Kobbie Mainoo does brilliantly to hold up play down the right, and then lay the ball into the path of Diogo Dalot.
The Portuguese defender opts to whip his cross over first time, and it's perfect for the arriving McTominay to power beyond Emiliano Martinez.
It triggers wild scenes of celebrations inside of the away section of Villa Park, and could - should - be enough for three points.
82. A lull in the stadium? Yes. A lull on the pitch? Most definitely. A lull on the touchline? You must be joking.
Unai Emery is going crazy down there, screaming, jumping and pulling the kind of shapes Mr Motivator would be proud of.
The Premier League is undoubtedly a better place with the Spaniard in it.
80. Garnacho sets off another mazy run infield from the left.
We knows he's to good for Cash, but he also accelerates past Tielemans to provide himself room to shoot.
It ends in disappointment though as he fails to get any power in his strike with the ball instead trundling through to his compatriot Martinez.
78. As we approach the final ten, there's the consensus that both sides have settled for the point on offer - which kind of makes a mockery of Erik ten Hag calling the contest a must-win.
Still, United have been really rocked by the need to replace the injured Luke Shaw at the break.
76. Casemiro spots his chance to grab the glory as he takes down a loose ball from 30 yards from goal.
The touch is good, the push forward is better, the resulting shot? Meh, not so much.
There was a surprise change at half-time for United as Erik ten Hag replaced Luke Shaw with Victor Lindelof at left back.
It can only be assumed Shaw has an injury because Leon Bailey went on to create United headaches down the left.
But when Villa threaten it's down the right as Matty Cash flashes in a cross which is met by Ollie Watkins.
However the striker's shot crashes off Onana's chest from point blank range.
If you can't be good be lucky!
Matty Cash is the third player to be booked when he brings down Rashford.
Villa are now well on top and Emery brings on striker Moussa Diaby for holding midfielder Boubacar Kamara.
The pay off is almost instant as Douglas Luiz strikes to draw Villa level after 67 minutes.
Leon Bailey's corner is fired goalwards by Lenglet and although Onana saves the ball breaks back to Bailey.
He picks out Douglas Luiz and the Brazilian beats Onana from close range.
Game on!
74. And Villa follow suit with a change of their own.
Like Rashford, Leon Bailey has been the pick of the attacking players on show, but his race is run and it's time for Youri Tielemans.
73. Marcus Rashford has looked a real threat at times today, but he's going to sit the final stages out.
Erik ten Hag decides to shore up proceedings with Scott McTominay.
71. Off the ball, Aston Villa substitute Moussa Diaby has been cautioned for bundling over Bruno Fernandes.
This game is anyone's to win now.
70. Garnacho goes close to restoring United's lead!
A darting run down the left leaves Cash for dead, and when he cuts back inside he lets fly with a low effort that beats Martinez's outstretched arm - but also beats the post.
67. It's all square at Villa Park!
Just like United's opener, the equaliser comes from a corner, but this is one painted with chaos and good fortune.
Two mis-kicks and a poor clearance sends the ball back out to Leon Bailey on the right, and when he darts a low centre back into a packed six-yard box, Douglas Luiz is in the right spot to lift into the roof of the net.
It's not a pretty goal, but it is a vital one, and is deserving of the midfielder's dance in front of the Holte End.
64. Boubacar Kamara will unable to continue, and he goes off to be replaced by Moussa Diaby.
Presumably it's a switch that will also bring about a change in a shape.
62. The action - which has been relentless since the restart - takes a pause after Kamara goes down clutching his knee.
The young midfielder, who suffered a bad knee injury last season, is seen to by Villa's medical team.
60. Matty Cash goes is cautioned for a tired dive in on Rashford after the Manchester United forward had easily twisted around and away for him.
The Villa right-back can have few complaints.
59. From defending a corner, Villa do everything right on the counter - until the final ball when Bailey attempts to slip in Ramsey.
Whether a slightly overhit pass or a miscontrol, the ball slides off the midfielder's foot and into the grateful hands of Onana.