Manchester United put in their worst first-half performance at Old Trafford in more than 22 years during the 3-1 loss to derby rival Manchester City in the Carabao Cup semi-final first leg.
The Red Devils were 3-0 down when the whistle was blown for half-time on Tuesday night, marking the first time they had conceded three goals at home since a game against Middlesbrough in May 1997.
Bernardo Silva put City ahead with a stunning long-range shot in the 17th minute, as he cut inside and curled the ball into David de Gea's top left corner.
United continued to try to hit City on the counter-attack, but the away side took a commanding lead in the tie with two swift moves.
In the 33rd minute, Silva played a magnificent through ball to release Riyad Mahrez, who rounded De Gea and slotted into the empty net.
And the Red Devils nightmare got worse six minutes later as a flowing City counter-attack saw Kevin De Bruyne's cross rebound off Andreas Pereira into his own goal.
Ole Gunnar Solskjaer's side managed an improved performance in the second half, pulling a goal back through Marcus Rashford, but still face an uphill battle in the second leg at the Etihad Stadium on January 29.
The last 15 teams that have won away in the first leg of the Carabao Cup semi-final have all progressed to the final.
For Pep Guardiola, it was an important victory after City were turned over 2-1 by United at home in their Premier League encounter during December.
Their first-half performance marked the 13th time a City team under Guardiola had accumulated at least a three-goal lead at half-time. Tottenham are the next best English side in that timeframe, but Spurs have accomplished the feat just four times.
It was also another strong result for City at the home of their greatest rival, with the blue side of Manchester having won seven of their last 10 away matches at the Theatre of Dreams (D1 L2) in all competitions, as many as in their previous 42 visits to Old Trafford.
Progression to the final would see City shoot for their third consecutive Carabao Cup title and their fourth in five seasons.