An Alexandre Lacazette goal was enough to give Arsenal a narrow, yet important, 1-0 win over Olympiacos in the Europa League last-32 first-leg clash played on Thursday night.
The Frenchman converted a Bukayo Saka cross with 10 minutes to go in a well-balanced clash that could have easily gone either way.
The hosts started the match brightly and should have grabbed the lead with only three minutes on the clock, Mathieu Valbuena forcing a wonderful save from Bernd Leno with a powerful shot that was headed for the bottom right corner.
They got yet another chance a minute later, this time an unmarked Masouras directing his header over the bar from Valbuena's cross.
Arsenal settled well into the match and controlled play even better, and should have gone ahead on the 21st minute only for Alexandre Lacazette to miss a clear chance.
The Frenchman over-hit a pass from Gabriel Martinelli, who managed to track it and keep it in play before laying it back to the Gunners' number nine only for him to blast it wide.
Arsenal then went through a scary moment on the 25th minute after a low cross from Masouras caused problems inside the box, but luckily the ball bounced off Leno and David Luiz managed to scramble it away.
Clear-cut chances then became far between as the first half wore on, with Lacazette trying his luck from outside the box on the 43rd minute but his shot was well blocked.
Three minutes into the second half Arsenal got a chance to score the opener following a weak clearance from the home side, but Aubameyang could not make contact with Saka's well-delivered cross at the far post.
David Luiz then unleashed a ferocious left-foot shot towards goal on the 54th minute, but the ball skidded off the wet turf and went harmlessly wide.
Arsenal continued to dominate play and kept pushing the hosts and were unlucky not to take the lead on the 63rd minute.
Xhaka floated in a lovely cross towards Lacazette, but the Frenchman could not connect properly with his header and the ball seemed to have touched Ba's arm as it rolled out but there was no penalty awarded.
The lively Valbuena then delivered a lovely cross into the box but Leno made a crucial jump to clear the danger with Masouras lurking.
The match became entertaining going into the last 20 minutes with end-to-end action and seemed it could go either way.
Arsenal kept knocking on the hosts' door and seemed the more likely to score going into the final stages of the match.
It was to happen with 10 minutes to go as Lacazette got to the end of a Saka ball that was played between the defenders to give the Gunners the lead on the 81st minute.
Three minutes later Arsenal poured forward on the counter-attack and Aubameyang picked out Lacazette in space, but the striker's shot was well saved by Sa.
Sokratis then headed the resulting corner against the crossbar, before going down clutching his hamstring but after some treatment, he was allowed to continue.
There were four added minutes but no more goals as Mikel Arteta's side grabbed an important win ahead of the return leg at the Emirates.