Arsenal 3-1 Valencia: 5 things we learned

#2. Marcelino gets his tactics all wrong as Valencia exposed

Marcelino watches on as his side, who were threatening in flashes, ultimately failed

You can understand Marcelino being wary of Arsenal's threats, particularly with their home advantage and given Unai Emery's Europa League pedigree to boot. However, that's not an adequate excuse to justify why he opted to change his tactics specifically for this game - where Valencia fielded six defenders - and were inviting pressure on themselves for sustained periods in both halves.

Other than a 15-minute spell at the start of both halves, Los Che found themselves swamped in their own area and if not for some wasteful finishing on Arsenal's part, would probably have no chance of recovering their deficit next Thursday.

Fullbacks Gaya and Piccini are both adept at flying forward as well as defending when called upon, so they were both expected to start as normal. But fielding four central defenders, playing one of them in defensive midfield and watching that unfold felt like a mistake Marcelino's men could never really recover from.

Former Arsenal man Gabriel was arguably their best defensive performer and unsurprisingly too, on his return to the Emirates. Argentinian duo Ezequiel Garay and Facundo Roncaglia partnered him in central defence, while goalscorer Diakhaby was shifted forward into a defensive-midfield role.

I can understand him wanting to use the players available at his disposal, but with Geoffrey Kondogbia sidelined and Francis Coquelin suspended, why not start Daniel Wass in midfield as usual? The game was crying out for his presence - not least after Diakhaby's booking 30 minutes in and despite a 20-minute cameo, he was one of their few bright sparks on a forgettable evening.

Now they have it all to do in the second leg next week and it's partly down to Marcelino's baffling tactical decisions, which left their backline under needless levels of attacking pressure while relying on counter-attacks to create chances once the game settled down.