"Who was the team in red?" he asked.
For a Middlesbrough team that had flopped in previous home games destroyed United with a superb display of attacking football.
Boro raced into a 3-0 interval lead and refused to let go, especially after the outstanding Gaizka Mendieta had scored a fourth goal.
This best of season display raises hopes of Middlesbrough climbing the Premier League table and mounting a strong challenge for the UEFA Cup.
For United, though, there are some serious questions to be asked after a shambles of a performance.
United can forget about getting anywhere near Chelsea in the battle for the top prize. The main priority for manager Sir Alex Ferguson will be to raise confidence after a horror show for the United fans.
The many visiting fans left the ground in droves before the final whistle.
But for Boro supporters it was a night to remember – a night in which they battled for every ball and piled up the goals.
Mendieta set Boro on the way with a superb goal after two minutes. The Spanish international hit a shot of tremendous power and accuracy from 30 yards.
Goalkeeper Edwin Van der Sar could only get a touch to the ball as it flew into the corner of the net.
Middlesbrough were without skipper Gareth Southgate and Ugo Ehiogu, two of the most experienced central defenders in the Premiership. But former Derby County defender Chris Riggott and local product Matthew Bates rose to the occasion in brilliant style.
Jimmy Floyd Hasselbaink, who was captain for the night, put Middlesbrough further ahead midway through the half when he held off the challenge of Rio Ferdinand in the penalty area and shot into the net.
The home fans could hardly believe their eyes and they taunted United with the chant of "easy, easy."
The game was being played at a tremendous pace with Middlesbrough always looking the more dangerous.
Mark Schwarzer denied United striker Ruud van Nistelrooy at the near post just before the break but it was the only serious save the Australian international was called upon to make in the 90 minutes.
Steve McClaren's side piled on the agony for Manchester United with a penalty goal just before the break. There was a blatant foul by substitute Kieran Richardson on Stuart Parnaby but for some reason the visitors protested vigorously.
Ferdinand and Van der Sar went across to thelinesman to protest but their actions were foolish bearing in mind it was a cast-iron penalty.
Van der Sar tried to put off Yakubu by wandering off his line in an act of gamesmanship but Middlesbrough's leading scorer nonchalantly stroked the ball into the net.
Middlesbrough suffered a blow when summer signing Fabio Rochemback was carried off on a stretcher with the ever reliable Doriva taking over.
The Teessiders, however, refused to lose their grip on the game. When United piled on the pressure there was never any real conviction about their attacking play.
Middlesbrough rubbed salt into their wounds when Mendieta crowned his brilliant performance. Yakubu pulled the ball back from the left for the unmarked Spaniard to dart forward and shoot into the net.
United substitute Cristiano Ronaldo pulled a goal back for the visitors in stoppage time when he headed in from a right-wing corner by skipper Paul Scholes. It could not even be considered a consolation goal.
MAN OF THE MATCH: Gaizka Mendieta (Middlesbrough) - Apart from scoring two goals, the Spanish international proved a class act in Boro's best display of the season. He was behind most of Boro's best work and capped a brilliant display with two well-taken goals.