For Arsenal, here was the evidence of how far they have fallen behind Europe's elite. Arsene Wenger's team were out-passed, out-thought and, ultimately, outclassed. They are almost certainly out of the competition and even in a season when they have encountered so much turmoil it was staggering to see the deterioration of this team.
They were dishevelled to the point Milan should have turned it into an even more harrowing ordeal. Arrigo Sacchi, the former Milan coach, had told Gazzetta dello Sport this was "the worst Arsenal side in 10 years", and Wenger, usually so protective of his team, was unsparing in his condemnation.
Wenger's team had barely been recognisable from the side that won here so thrillingly in 2008. They lost their nerve as soon as Kevin-Prince Boateng lashed in the opening goal and, by the end, it was difficult to identify a single redeeming feature.
Their passing lacked accuracy, they did not close down the ball, their defending was atrocious. Sacchi's assessment felt brutally close to the truth on a night when Milan were superior in every department. This was the evening when Robinho reminded us why Manchester City once made him the most expensive footballer in Britain, an elusive opponent contributing a goal either side of half-time.
Zlatan Ibrahimovic was even more impressive, as though affronted by the accusation that he sometimes vanishes at this stage of the competition. This was a footballer at the point of maximum expression and it was his penalty that made it 4-0 and extinguished any faint hopes of Arsenal turning the tie upside down in the return leg on 6 March. "Let's be realistic," cautioned Wenger. "We don't play in a dream world. Maybe we have 2% or 5% statistically (to advance). "We have to show a completely different performance and you never know. But, realistically, we are out of the competition."
Roman Shirokov helped fire Zenit St Petersburg to a 3-2 win against Benfica in freezing conditions in their Champions League last 16 first-leg match on Wednesday. The midfielder equalised for the Russian champions in the 27th minute, shortly after Maxi Pereira had put the Portuguese side ahead from a free kick, and he grabbed the winner two minutes from time.
Sergei Semak fired the home side in front again midway through the second half before Oscar Cardozo made it 2-2 for Benfica, setting the stage for Shirokov's late strike.