United spurned the chance to all but seal a 20th league title with victory against neighbours Manchester City on Monday night.
Instead, a goal on the stroke of half-time by Vincent Kompany handed the Blues three points and the advantage in this thrilling title race.
Now, with just two games to play, both sides are level on 83 points. But City boast a vastly superior goal difference and are hot favourites to collect a first league title since 1968.
Nothing's decided yet, mind you. Roberto Mancini's men still face a tricky trip to Newcastle next weekend before welcoming relegation-threatened Queens Park Rangers to the Etihad on the final day of the season.
Judging by the scenes at the final whistle on Monday night, though, City fans are convinced their long wait for domestic supremacy is over. They certainly won this battle at the Etihad, as United struggled to create any clear-cut chances.
Of course, played under the spectre of “the biggest Manchester derby ever”, the match was always in danger of drowning in its own hype. In fairness, though, while there have been many more entertaining meetings between the sides in recent years – the 4-3 at Old Trafford, anyone? - this contest served up its fair share of drama, including a tense final 10 minutes and a touchline spat between the two managers.
Sir Alex's team selection was the first big surprise of the night, with his decision to make four changes to the side that drew 4-4 against Everton eight days earlier raising plenty of eyebrows.
In came Chris Smalling and Phil Jones (for the injured Jonny Evans and Rafael), while Ji-sung Park was handed his first league start since