Will Arsenal ever learn?

Arsene Wenger's side knew nothing other than victory would do after defeat by Dinamo Zagreb in Croatia in their opening game - and with two meetings with group favourites Bayern Munich still to come.

Instead it was a dreadful night for Arsenal, who must now become the first team since Galatasaray in 2012-13 to lose their first two group games and still reach the knockout stage.

The Gunners' display was summed up by the wretched first-half own goal conceded by David Ospina - preferred to Petr Cech in goal - when he dropped Kostas Fortounis's corner into his own net after Theo Walcott equalised Felipe Pardo's deflected shot.

Alexis Sanchez gave Arsenal hope with a 65th-minute header only for Alfred Finnbogason to restore Olympiakos's lead within a minute.

Arsenal's defensive naivety was best encapsulated by the manner they went out to a very average Monaco side in the last 16 of last season's Champions League.

The Gunners pulled a goal back to make the score 2-1 in injury time in the first leg - then promptly rushed forward like lemmings in search of an equaliser, only to concede the decisive third goal that effectively put them out.

The question now is will they ever learn? Will they ever cure the defensive frailty and general vulnerability that leaves them exposed at this level?

Arsenal were victims of a deflection and a crass goalkeeping error for Olympiakos's first two goals - but the soft underbelly was on show again for the third, so easily unpicked as Finnbogason steered in the winner.

They simply did not show the maturity or composure to settle themselves. And if they cannot do that by now you have to wonder when they ever will.

Amid a night of unrelenting gloom, the only shafts of light for Arsenal and their supporters were Walcott and Sanchez.

The Englishman continued his development as a striker with another goal, his second in successive Champions League games after scoring his 12th in 13 Premier League matches at Leicester City on Saturday.

Sanchez scored a hat-trick at Leceister and he was lively throughout, heading the second equaliser only to see Olympiakos score their third almost immediately.

In reality, this is to clutch at straws because this was a desperate Arsenal display elsewhere.