Arsenal 2 Olympiacos 3

A goalkeeping howler from David Ospina summed up Arsenal’s night as they crashed to a home defeat that left their Champions League campaign in tatters.

Ospina, one of five changes to the side that beat Leicester on Saturday, misjudged a corner from Kostas Fortounis and dropped the ball over the line to gift Olympiacos a 2-1 lead.

Theo Walcott had cancelled out Felipe Pardo’s opener prior to Ospina’s mistake and, although Alexis Sanchez made it 2-2 midway through the second half, Alfred Finnbogason sealed victory for the Greeks.

The result left Arsenal bottom of Group F after two games, with a double header against Bayern Munich to come and lengthening odds against them progressing to the knockout stage.

Billed as a must-win game for Arsenal, the gentle early tempo did little to suggest that kind of urgency as neither side created much in the way of clear openings.

The home side’s only real opportunities came on the counter-attack, with Sanchez sliding a ball through for Alex Oxlade-Chamberlain, who held off his marker but blazed into the side netting.

Soon afterwards Sanchez played Walcott through, but his tame effort was comfortably gathered by Roberto – and it was the Greek side who broke the deadlock 12 minutes before half-time.

Sloppy defending enabled Pajtim Kasami to win a corner and the ball was played directly to Pardo, whose drive from the edge of the box struck Oxlade-Chamberlain and deflected past Ospina.

The Gunners delivered their response just two minutes later as Sanchez threaded another through ball for Walcott, whose drive went through the keeper for the equaliser.

But Roberto’s error suddenly seemed trivial five minutes before the break when Fortounis sent over an inswinging corner that Ospina spilled behind the line.

There were ironic cheers for the Arsenal goalkeeper when he gathered a routine shot from Olympiacos substitute Finnbogason early in the second half.

The home side sent on Aaron Ramsey with half an hour remaining and the Welshman almost made an immediate impact with a pass that might well have brought his side level.

Sanchez collected the ball and crossed for Per Mertesacker, whose effort was beaten out by Roberto and driven goalwards again by Santi Cazorla, only for Omar Elabdellaoui to block it on the line.

Arsenal restored parity when Sanchez headed in Walcott’s cross – but promptly surrendered it again as Pardo crossed for Finnbogason to glance the ball across Ospina into the far corner.

The Gunners had chances to strike back, but Roberto clawed away free-kicks from both Cazorla and Mesut Ozil and, despite late pressure, the visitors clung on.

Arsenal: Ospina; Bellerin (Campbell 85), Gabriel, Koscielny (Mertesacker 57), Gibbs; Cazorla, Coquelin (Ramsey 60); Oxlade-Chamberlain, Ozil, Sanchez; Walcott