Arsenal’s Champions League hopes were dealt a severe blow after suffering a calamitous 3-2 defeat at home to Olympiakos. Having lost 2-1 to Dinamo Zagreb on Matchday One, manager Arsene Wenger make it clear that his side now needed to take maximum points from their three home group games. But instead his side played with the kind of shambolic naivety that cost them so dearly in their last Champions League home match, in last season’s Round of 16 against Monaco.

Twice Arsenal were given chances to steady the ship when bouncing back from poorly conceded goals. After Felipe Pardo’s shot deflected past David Ospina, the Arsenal goalkeeper, again stepping in for Petr Cech in the Champions League, embarrassingly bundled a corner over his own goal line to cancel out Theo Walcott’s quick-fore equalizer. Alexis Sanchez appeared to have rescued his side at least a point when capitalizing on ferocious Arsenal pressure midway through the second half. Yet just a minute later the hosts allowed Alfred Finnbogason to net his first Champions League goal and secure Olympiakos a first victory in England at their 13th attempt.

Indeed, in just over 30 minutes Arsenal had allowed Olympiakos to score as many goals in England as they had done in their 12 previous visits. Arsenal had beaten the Greek side on three of those occasions, all in the past six seasons, as Wenger’s men continued a record of making it out of the group phase for 15 successive seasons. But the continuation of that streak is now under huge threat. Without a point from two matches, they now face home and away contests with Bayern Munich, who have sauntered to maximum points. At least one victory against the German giants could now be required. If not, then Olympiakos may well be waiting in the wings after one of the finest victories in their recent history.

From the off it was an engrossingly open contest, far too open from the perspective of the home side. Arsenal twice threatened dangerously on the break in the opening 15 minutes, first when Alex Oxlade-Chamberlain could only fire into the side netting and then when Theo Walcott shot tamely at Olympiakos goalkeeper Roberto.

But in a worrying sign for the London side, the visitors had also twice gone close to breaking the deadlock through Konstantinos Fortounis. Yet Wenger’s men failed to heed the warnings, and in the 33rd minute they were behind. Not for the last time in the contest it was inept Arsenal defending that did the damage. After failing to pick up Pardo on the edge of the box from a corner, Arsenal could only watch on in horror as the Colombian’s shot deflected off Oxlade-Chamberlain and into the net.

Arsenal would grant themselves an immediate reprieve with some equally poor play from Olympiakos at the other end. From Sanchez’s pass, Walcott struck and effort across goal that really should have been parried to safety by Roberto, but instead the former Atletico Madrid goalkeeper allowed the ball to bounce off him and into the net.

Not to be outdone, Ospina upped the comical goalkeeping stakes at the other end to leave Arsenal trailing going into the interval. Having stepped out of his goal to try and meet a corner, the Colombia No. 1 was caught out when it instead swung under his crossbar. Still, he should have comfortably kept it out, before instead patting it down just the wrong side of the line.

Given fresh impetus by the arrival of Aaron Ramsey off the bench, Arsenal pushed strongly in search of an equalizer and began to get up a head of steam around the hour mark. Some incredible last-ditch defending kept Olympiakos in front temporarily, but their resistance was broken in the 65th minute. Walcott’s cross into the box was perfect and Sanchez was on hand 10 yards out to head down and into the corner.

At that point there should have been only one winner. Arsenal’s extraordinary openness at the back, though, immediately proved their undoing. With suspect defensive positioning and no cover in front of the back four, Esteban Cambiasso was able to chip into the box for Pardo, who crossed for Finnbogason to turn past Ospina in front of Per Mertesacker.