After an early display of questionable defending, Arsenal regrouped themselves and regathered their purpose to overcome Valencia and take a 3-1 first-leg lead.
There were just eight minutes gone when Arsenal were caught cold by a free kick from Daniel Parejo.
Rodrigo volleyed it back across into the six yard box where Ezequiel Garay should have done better, but was thwarted by Sokratis.
It was only a temporary delay, though. Just two minutes later, Valencia took the lead from a set piece that reflects poorly on just about every member of the Arsenal back line, including goalkeeper Petr Cech.
Again, Parejo was the provider, finding Rodrigo at the far post, poorly marshalled by Sead Kolasinac. He headed it back across goal, where Mouctar Diakhaby waited, guarded by a further three Arsenal defenders, plus Cech.
Now Diakhaby is a huge chap, a giant of a player, capable of playing in central midfield or central defence, a rising star of French age group teams. Yet there are plenty of big men out there, and defenders deal with them all the time.
One of Arsenal’s men should have been a match for Diakhaby, have put him off balance, even if they couldn’t outjump him. Instead, he nodded the ball into the net as if surrounded by toddlers. Cech didn’t read the situation well, either. It was a terrible goal to concede; and it could have got
From Valencia’s next attack, Parejo tried a shot from 20 yards that Cech parried poorly, pushing the ball out, rather than into a wide area. Fortunately, Ainsley Maitland-Niles was on hand to mop up.
It was a swift, intelligent break that got Arsenal back into the game, Alexandre Lacazette feeding Pierre-Emerick Aubameyang, who sped clear of a sluggish back line, drawing Neto as he did. It was a poor decision by the goalkeeper. In coming out, he made Aubameyang’s next move obvious, and left his goal utterly unprotected. Sure enough, Aubameyang squared to Lacazette, who had continued his supporting run, and the Frenchman slotted the ball into the empty net.
This warded off a fan mutiny, and eight minutes later they were celebrating with even greater gusto. Again, Valencia came up short at the back, Neto most of all. The ball came in from Granit Xhaka on the left, Lacazette lost his man far too easily and was given a free header.
He steered it down, into the turf, a smart move – but Neto should have done better. He palmed the ball onto the post and it rebounded over the line before he had a chance to claw clear. Goal-line technology confirmed the good news, although why the assistant on the by-line couldn’t have done that with the naked eye is puzzling.