Arsenal fought the good fight, but ultimately capitulated to a superior Borussia Dortmund side at the Emirates Stadium.
It was the Gunners' first defeat since their humiliation way back on opening day against Aston Villa.
Arsenal and Dortmund matched each other's quality for stretches, but the Germans were the much more aggressive and robust side. Ultimately, the Gunners could not cope with the relentless pressure applied by Dortmund.
After a sterling run of form, Arsenal's momentum might be blunted a bit ahead of their most difficult stretch of the season. Let's look at six things we learned from the match.