Jose Mourinho took off Marcus Rashford and introduced Anthony Martial with 20 minutes left against Spurs and the match still goalless. Sections of Old Trafford seemed unhappy with the switch - despite the pace and trickery of the Frenchman and his burgeoning reputation as our go-to super sub.
Instead, the change was a masterstoke and proved the catalyst for United's match-winning surge as they finally broke down Spurs disciplined and dogged defence. Romelu Lukaku had a much better day at the office, and it was from his flick on that Martial raced through to finally break the deadlock.
It could easily have been Lukaku who was withdrawn and not Rashford - but Jose stuck with his big money signing and the decision paid dividends. He was well marshalled by Eric Dier, Toby Alderweireld and Jan Vertonghen for much of the game, but - through sheer persistence, determination and character, he made a crucial contribution to set up our late winner.
It was Martial's fourth league goal of the season, all of which have come as a substitute.
When he starts, his impact is minimal but he's proving a dangerous and match-changing weapon from the bench. It's a double dilemma for the opposition: having to deal with Rashford for the first 70 minutes before Martial is introduced to finish off stretched and tiring defences.
Mourinho had criticism to contend with for his tactical approach at Anfield a fortnight ago - but, here he made a tactical tweak that proved decisive. This was the biggest result of our season so far and a massive statement win against one of the other top sides that we desperately needed.
Spurs may have been missing talismanic striker Harry Kane but even without him, they are a side that possess talent and quality throughout their squad.
The fact that Kane was absent here should not make this any less of an impressive result for the team.
Another key man for United was the rejuvenated Ashley Young, who looks a player reborn under Mourinho's tutelage.
Employed as a left wing-back, he defended tirelessly and showcased his dangerous crossing ability that was his trademark under Sir Alex, as a flying winger.
Young received a fully deserved standing ovation from the Old Trafford crowd when he was taken off in stoppage time.
He was later voted as Man of the Match and has worked hard at turning around his United career when many thought he would be moved on.
After the shock defeat last weekend, United were much improved (but then again we couldn't have been any worse) and kept pace with leaders City who won again, 3-2 at West Brom.