The Gunners had a disastrous start to the game, as they survived a glaring open-goal miss from Ezequiel Garay, but did not learn from their early scare as Valencia took advantage of some statuesque Arsenal defending from a corner to take the lead through Mouactar Diakhaby's point-blank 11th-minute header.

But Arsenal regrouped and swiftly hit back after a sweeping counter-attack involving Mesut Ozil, Aubameyang and Lacazette finished with the latter scoring to round off a beautiful flowing team move.

That goal saw Arsenal visibly grow in confidence, and the London club took the lead on the 25-minute mark as Lacazette's header found its way past Valencia goalkeeper Neto, whose poor attempt at a save saw the ball cross the goal-line before he attempted to claw it clear. Goal-line technology eliminated any doubt as the goal was instantly given.

Lacazette spurned a trio of second-half chances to complete his hat-trick, missing a clear header from six yards out, then twice failing to beat Kepa after finding himself clean through on goal just after the hour mark.

And Arsenal were nearly made to pay 10 minutes later as Kevin Gameiro sneaked in behind the Gunners defence, but veteran stopper Petr Cech was alive to the danger and made a smart block.

But Arsenal's pressure paid off in the final minutes as, following a brilliant Neto save to deny Lacazette, Aubameyang finished excellently on the volley from an acute angle to give the Gunners a 3-1 victory and secure a crucial two-goal lead for the London side ahead of the return leg in Spain next Thursday.