Arsenal came away from their trip to Piraeus with a 3-1 victory over Olympiakos but Mikel Arteta was far from content with the performance from his side.
The Gunners took the lead thanks to a superb Martin Odegaard strike, his first goal for the club, but they were then pegged back as a mix-up between Bernd Leno and Dani Ceballos saw Youssef El Arabi equalise.
Gabriel scored a stunning header to put the visitors back in front before an excellent hit from Mohamed Elneny sealed a big win in the first leg of the last 16 tie.
While the result is an excellent one, Arsenal displayed some of their regular failings in presenting chances for their opponents, largely from mistakes when playing it out from the back.
Arteta knows that they need to cut out these errors if they are to progress in league and cup competitions.
‘I want to be much more ruthless and as a team I don’t want to give anything to an opponent,’ said the Spaniard after the match. ‘I am happy with the result but I’m not satisfied with how we controlled the game.
‘The chances we have conceded are coming from ourselves. That’s positive because when we stop it, we will be stronger. The reality is that we have to stop it immediately.’
Arteta said there is nothing wrong with his plan of playing out from the back, there just needs to be better choices made as to when to do so.
‘We have to stop making the errors that cost goals because you cannot sustain that at this level,’ he told BT Sport.
‘It’s not concentration, it’s about when you play the ball, it’s not about the structure, it’s not about stopping trying to play the way we play, because this is us.
‘It’s about identifying when we have to do it and how we have to do it.’
Arsenal host Tottenham in the north London derby on Sunday afternoon before taking on Olympiakos in the second leg at the Emirates next Thursday.