Manchester City flew out of the blocks, scored the first goal, an absolute peach, and it looked like being just another Manchester Derby dominated by the team in blue, with Manchester United unable to find anything resembling their recent groove.
Then, a quick counter-attack and Ashley Young scored, and from there everything changed. Suddenly Manchester United were playing like the Manchester United of the past few months in the English Premier League again, and Manchester City started to look like the Man City that have gone down in three of their last three away games.
Roared on by a louder than usual Old Trafford crowd, Manchester United produced a stirring Derby performance, banging in four goals to annihilate Manchester City's spirt and any remotest of hopes of a title challenge.
Marouane Fellaini, Juan Mata and Chris Smalling joined young on the scoresheet, after Sergio Aguero had given City the perfect start at Old Trafford.
Louis Van Gaal was always going to go with pretty much the same lineup that has worked wonders of late, and so he did, with that midfield of his again doing the business to overwhelm the broken and bruised City.
It looked like Manchester City might find their mojo again in the fixture they have enjoyed so much recent success, though, as they attacked the United defence right from minute one. That brisk start was rewarded by a goal as well, and a glorious one it was too.
Left-back Gael Clichy, who would later have a much more torrid time in defence, made a brilliant run upfield and gave the ball to James Milner, who then found David Silva in space in the left channel. The diminutive Spaniard then looked up, saw Aguero's run and put the ball on a plate for the Argentine to tap into an empty net on eight minutes.
That goal was no more than Manchester City deserved, but this Manchester United beast is a different one from the ones they have faced in the last few games. United knew a goal and they were right back in it and that goal came courtesy some luck and some brilliance from Ander Herrera.
A clearance from David De Gea towards, who else, Fellaini saw the Belgian floor Pablo Zabaleta, freeing up Herrera to run down the left and pick a beautiful low cross for Young to try and turn in. Clichy did well to prevent Young from getting enough of a contact to score first time, but unfortunately for the City defender, the ball deflected back to Young, who then had the simplest of jobs of placing the ball into an empty net.
The day would only get a lot, lot worse for Manchester City as United, much more confident now and controlling the game, took the lead for the first time via the head of their target man Fellaini. Young was the assist-maker on this occasion, playing a really nice cross with his right foot from the left, with Fellaini getting on the end of the ball at the far post and powering a header past Joe Hart.
Suddenly, with less than half-an-hour played, United were 2-1 in the lead, and that one-goal lead lasted until the 67th minute, with Manchester City never really looking capable of breaking down the opponent's defence. Mata, after starring in the derby against Liverpool three weeks ago, made a big impact in the Manchester Derby as well, latching onto a through ball from Wayne Rooney, before calmly slotting the ball through Hart's legs.
If Manchester City were to have any chance of getting at least a point out of Old Trafford, they had to score immediately after the Mata goal, but, instead, it was United who did that, with Smalling heading home a Young freekick to make it 4-game-set-and-match-1.
Aguero would grab a late consolation, after the home team were down to ten men with Michael Carrick going off through injury and all three substitutes used, but by then the derby was done and Manchester United had pulled four away from their neighbours and to within one of Arsenal again.