Carlo Ancelotti couldn't even face Eduardo Camavinga after the Real Madrid star's meltdown saw him sent off vs Arsenal.
The Gunners had already wrapped up the first leg in emphatic fashion, leading 3-0 in the dying moments of the game.
But things went from bad to worse for the European champions when Camavinga got himself dismissed for petulantly kicking the ball away in the final seconds. The France international had already picked up a yellow and so was given his marching orders before the final whistle was blown.
Camavinga was already set to miss the second tie thanks to an accumulation of yellow cards in the competition, but nevertheless, his manager Ancelotti was less than impressed. "Talk about a loss of discipline. Right here is a prime example," ex- Arsenal defender Matt Upson said on BBC Radio 5 Live.
" Carlo Ancelotti looks the other way as Eduardo Camavinga walks down the tunnel. It is a head loss moment and the referee has no option but to send him off."
Madrid headed to north London hoping to secure a first-leg lead to take back to the Bernabeu next week and to bounce back from a disappointing defeat to Valencia in La Liga. But after a tight first half, Arsenal ran riot in the second, scoring three times in 17 minutes to put them in total command of the tie.
Declan Rice was the hero for the Gunners, blowing the quarter-final tie wide open with a pair of stunning free-kicks. Mikel Merino then made it three to ensure Arsenal travel to the Spanish capital in a commanding position.
Rice was quick to point out that there would be no complacency ahead of that second leg, with disconsolate Real Madrid players refusing to count themselves out.
Lucas Vazquez said on a potential comeback: "It's complicated, of course, but if there's a team in the world that can turn this around, it's us. In our stadium, with our fans. It's going to be a different game than this one, and together we'll pull it out."
Raul Asencio gave an honest insight into the away dressing room after suffering a second defeat in a matter of days: "We're p***ed off, it wasn't what we expected, but we're convinced we're capable of turning it around, we're Real Madrid, and we're already positive about that."
Asked how they can rescue the tie, the Madrid defender added: "By being a team, working hard, changing our attitude. But if there's any team in the world that can turn this around, it's us. I'm convinced, and the team is convinced, that we're going to turn this around."