Bruno Fernandes scored his first Manchester United hat-trick as Ole Gunnar Solskjaer's side overpowered old rivals Leeds to make the perfect start to the new Premier League season.
The Portugal midfielder opened the scoring on the half-hour mark at a packed Old Trafford, but Luke Ayling's thunderous strike drew Leeds level early in the second half.
Mason Greenwood restored the hosts' lead with a crisp finish less than two minutes later, before Fernandes' low shot was ruled to have crossed the line by referee Paul Tierney after a check of goalline technology.
The 26-year-old quickly completed his hat-trick with a thumping finish from Victor Lindelof's pass, before Fred added United's fourth goal in 14 minutes from Paul Pogba's cross - the Frenchman's fourth assist of the afternoon.
It was Fernandes' first hat-trick since he moved to Old Trafford in January 2020 and only the second by a Red Devils player since Robin van Persie's title-winning effort against Aston Villa in 2013.
But the game was also a personal triumph for Pogba.
The France midfielder's future has been the subject of intense debate as he enters the final year of his contract.
But his four assists included a sublime pass for Greenwood's goal, and he left the field to a standing ovation 15 minutes from time as £74m new-boy Jadon Sancho was introduced for his debut.
Fernandes' last hat-trick was for Sporting Lisbon in an 8-1 hammering of Belenenses in front of just over 5,000 in May 2019.
Although the Portuguese has assumed hero status since moving to England, this was only the fourth time he had played a Premier League game in front of capacity crowd at Old Trafford.
After a disappointing Euro 2020, any concerns about his impact at domestic level have been completely dispelled.
His opener was excellent as he ran on to Pogba's first-time pass, controlled a bouncing ball in the Leeds area, then put enough power into his shot to take it into the net despite Illan Meslier's half-save.
Another Pogba pass offered Fernandes the opportunity to sit Meslier on his backside as he turned sharply before hitting a low shot goalwards that referee Tierney was correctly informed had crossed the line before Ayling cleared.
Fernandes' third was route one. Lindelof's pass fell perfectly for the forward, who allowed the ball to bounce before crashing it into the net.
It meant he followed Anthony Martial as the only Manchester United player to score a Premier League hat-trick since Van Persie - and the first to do it in front of fans.