Walcott got on the end of Jack Wilshere’s cross to give Arsene Wenger’s side an early lead in the first-half.
And while that goal gave the visitors the confidence and composure to control the game, it also appears to have rattled the BATE Borisov back line… in particular the goalkeeper, Denis Scherbitski.
With Arsenal looking to press the Belarusian champions, Scherbitski made a horrendous attempt at a pass to his full-back… a ball which only found an on-rushing Walcott.
Despite being criticised throughout his career for “not having a footballing brain”, the England international made no mistake, sliding the ball beyond the red-faced shot-stopper:
Arsenal have since scored a third goal through Rob Holding, the defender’s first since signing from Bolton last year.
However, the home side replied with a strike of their own almost immediately, with Mirko Ivanić nodding the ball beyond David Ospina.