Arsenal took a big step towards the Europa League last 16 as Alexandre Lacazette's late strike secured a 1-0 win away to Olympiakos in the first leg of their round-of-32 tie.
Lacazette converted from close range in the 81st minute after Bukayo Saka had latched onto Pierre-Emerick Aubameyang's pass and sent the ball across the six-yard box.
Arsenal had survived some awkward moments before that, with Bernd Leno making some fine saves, but they could have put the tie out of Olympiakos's reach in the closing stages, with Lacazette spurning another opportunity and Sokratis striking the woodwork with a header.
The Gunners still take a lead back to the Emirates Stadium, though, extending their unbeaten run to nine games under Mikel Arteta, and they will be confident of reaching the next round of the Europa League when they welcome Olympiakos to the Emirates Stadium for next week's second leg.
Olympiakos: Sa (7), Elabdellaoui (6), Semedo (6), Ba (6), Tsimikas (6), Guilherme (6), Camara (6), Bouchalakis (6), Masouras (6), Valbuena (8), El Arabi (6).
Subs: Lovera (6), Fortounis (6)
Arsenal: Leno (8), Sokratis (7), Mustafi (7), Luiz (8), Saka (8), Xhaka (7), Guendouzi (7), Willock (7), Martinelli (6), Aubameyang (7), Lacazette (8).
Subs: Ceballos (6), Pepe (6), Maitland-Niles (6)
Man of the match: Saka
How the Gunners got their win
Arsenal came into this game on the back of Sunday's impressive 4-0 win over Newcastle, but they started slowly at the Karaiskakis Stadium, with Olympiakos twice going close to scoring inside the opening four minutes.
First, Leno was forced into a smart save from Mathieu Valbuena after the Frenchman was left unmarked on the left-hand side of the Arsenal box.
Then, just moments later, Giorgos Masouras spurned an even better chance when he headed Valbuena's inviting cross over the bar from close range.
Arsenal, who fielded a strong team despite Arteta making five changes to his side, were fortunate to survive those early scares, but they grew into the game and should have scored themselves when Lacazette fired wide from Gabriel Martinelli's cut-back midway through the half.
Olympiakos continued to threaten on the counter-attack, however, with Leno reacting smartly to prevent David Luiz from deflecting a Masouras cross into his own net.
And Leno was called into action several more times after the break, making a fine reaction save from Ousseynou Ba's close-range header, albeit before the Olympiakos man was flagged for offside, then managing to smother a powerful free kick from the dangerous Valbuena.
It seemed the Gunners were in for a nervy finale, but a clinical counter-attack changed the game. Aubameyang did well to control a long-range pass and find Saka, and the 18-year-old, who produced another excellent all-round performance, was able to pick out Lacazette for an easy finish.
It was Lacazette's second goal in two outings following a nine-game drought, and he was denied another by Olympiakos goalkeeper Jose Sa following another rapid Arsenal counter-attack soon afterwards.
It was then Sokratis's turn to go close, the defender rattling the crossbar from a the resulting corner.
Olympiakos attempted to rally in the closing stages, but Arsenal showed resilience to secure a third consecutive clean sheet and secure a victory which, as well as putting them in a strong position to advance to the next round, adds to the growing sense of optimism that they could yet salvage something from their season.
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What the manager said...
Arsenal boss Mikel Arteta: "It's a really good result. To win here is really difficult. Credit to the lads. We suffered in the first 10 minutes. After that we started to have more control of the game and create some good opportunities.
"In the second half we controlled the game much better and we had chances. I think we could have put the tie in a much better position. It's still good but we had clear chances with top players and we expect them to put the ball in the net."
Opta stats: Saka the assist king
- Overall this season, Bukayo Saka has nine assists to his name in all competitions - more than any other Arsenal player.
- Alexandre Lacazette has found the net in each of his last two games in all competitions for Arsenal, after failing to score in each of the nine before that.
- Arsenal are unbeaten in six away European games for the first time since a run of eight which ended in September 2006.
- Arsenal remain the only Premier League side yet to lose a game in all competitions in 2020 (P9 W5 D4).
Arsenal return to Premier League action against Everton on Sunday, live on Sky Sports Premier League from 4pm, ahead of the 4.30pm kick-off. The second leg of this Europa League tie will take place at the Emirates next Thursday on February 27.