Gabriel Magalhaes and Mohamed Elneny spared Arsenal's blushes against Olympiakos after the Gunners did their best to undo all their hard work for a second fixture running.
Arsenal took the lead in the first half through Martin Odegaard, who opened his account for the Gunners with a thunderous effort from range.
But Arsenal repeated their performance against Burnley by giving the ball away just outside their area, gifting Youssef El-Arabi an easy opportunity to score.
Arsenal battled back ten minutes before the end to put themselves in the driving seat for the second leg at the Emirates, with Gabriel scoring his first goal in Europe to secure the win.
Elneny put the cherry on the icing with another long-range effort late on.
Here are five talking points from the match.
Self-inflicted mistakes still present
The last time out it was Granit Xhaka who broke the first rule of football by passing the ball across goal.
The inevitable interception resulted in a goal and two dropped points from Arsenal.
This time Real Madrid loanee Martin Odegaard played a sloppy sideways ball that was intercepted and led to a shot on goal around the 20-minute mark.
Fortunately for Arsenal on this occasion, Bernd Leno was able to make a comfortable save.
Twenty minutes later and it was David Luiz's turn to squander possession in the Gunners box. Again, Arsenal were very lucky to get away with not conceding.
In the second half, the luck finally ran out after Dani Ceballos was dispossessed just outside the Arsenal area, Leno was caught out of position, and the ball hit the back of the net.
In the grand scheme of the night, it's not a major problem. But all these little mistakes add up over the course of a season, and currently, the risk is outweighing the reward.
If the Gunners are to push on and become a great team once again - all the ingredients are there - then they have to stamp out the sloppy and downright frustration mistakes present each and every week.
Oh my Gaard
There was much fanfare around Real Madrid forward Martin Odegaard signing on loan for the Gunners in the summer transfer window.
The youngster has carried the weight of his potential on his shoulders for the past few years but is yet to reach the dizzying heights predicted for him when he joined Los Blancos in 2015.
His loan move to Arsenal has enabled him to continue his development in another country, but it already appears clear that Mikel Arteta won't want to send him home.
In many ways, Arteta has built his Arsenal team around the Norwegian this season, with Emile Smith-Rowe shifted out of the spotlight to make way for the new number 10.
Kieran Tierney has also made a point of trying to find Odegaard with his crosses.
Throughout the Olympiakos match, the Scottish left-back sprinted to the byline before firing his cross back on himself in the hope of finding Odegaard's run into the box.
He succeeded on more than one occasion, suggesting this is something Arteta has devised in training.
Odegaard's moment of the match came in the first half when he took full advantage of Olympiakos' reluctance to close him down.
To be fair to the Greek side, there didn't seem to be much on for the Norwegian who showed why he is so highly rated by smashing a ball from distance into the roof of the net.
Not a bad first goal for your new club by any measure.
Partey pooper
Thomas Partey is Arsenal's biggest recent signing and when he's on his game you can see why Mikel Arteta and co. were so keen to splash the cash on him.
But injuries have blighted the midfielder this season, which has been damaging for Arsenal and his confidence.
Partey has only made 15 appearances in all competitions for the Gunners this campaign, and more worryingly is his apparent inability to play a full match.
This is preventing him from really getting to know his team-mates on match day, and he hasn't really been able to form any sort of partnerships as a result.
Against Olympiakos, Partey was busy and had a lot of the ball.
But barring a shot on goal - the ball nearly cleared the stadium it was smashed so high and wide - the midfielder was largely ineffective before making way on the hour mark.
Partey looked frustrated as he was taken off, but there can be no real questions over Arteta's decision.
Pierre pressure?
Arsenal forward Pierre-Emerick Aubameyang is world-class on his day.
But the Gabon international hasn't been himself this season and offered very little in the final third for the Gunners on Thursday night.
The striker found himself in the Olympiakos box with the ball at his feet on more than one occasion, but the former Dortmund star never had a breakthrough moment.
It would be easy to criticise Aubmeyang for his alarming lack of presence against Olympiakos.
But Arsenal have changed their shape in recent weeks, with much of their attacking play coming via Odegaard through the middle.
This doesn't appear to complement Aubameyang's attacking movement and the once dangerous forward has been largely ineffective in recent weeks by his usual standards.
In short, Arsenal missed Alexandre Lacazette, and this showed when things livened up after he came on.
Put a Sok in it
Sokratis faced Arsenal for the first time since leaving for Olympiakos in the summer transfer window, but it wasn't a happy reunion for the Greek.
The centre-back didn't have a bad game by all accounts, but his side certainly have a lot more work to do in the second leg at the Emirates.
Ahead of the match Olympiakos winger Bruma revealed Sokratis had been spilling secrets on the Gunners.
Whether he had or not remains to be seen as Olympiakos were largely second-best on the night.
And Mikel Arteta would have seen nothing from Sokratis on the night to have him doubting whether he made the wrong decision letting the centre-back leave.
