After a brief opening flurry from West Ham, the story of the first half was of Arsenal attacks, with Olivier Giroud repeatedly failing to get on the end of a series of crosses from Mezut Özil, Kieran Gibbs and Bacary Sagna.
Arsenal attacked in waves, with overlapping full-backs and quick, penetrative midfielders breaking forward to support Walcott, and their supremacy had the added effect of spreading anxiety among the Villa players.
Moments later, as Arsenal attacked, five red-shirted players swarmed into the box, Ramsey chief among them, only for Anderlecht to scamper away through a vacated midfield and score a schoolboy-level, two-touch equaliser.
A couple of minutes later, Arsenal attacked again, with more confidence and flair this time, as though they were playing an elegant game of hot potato, and their French forward Alexandre Lacazette fizzed in another goal from a few yards out.
Graham Dorrans also twice scuffed low efforts wide after the interval but the second half was a procession of Arsenal attacks as West Brom's solid resistance was broken.
