The Gunners eventually broke the deadlock in the 32nd minute as the hosts broke on the counter led by Alex Iwobi, who slid the ball to Aubameyang for the close range finish.
"Great to start the Europa League campaign with a win", Iwobi tweeted.
"Fans were awesome, Emirates was a party tonight".More news: Cleveland Browns: Is it too early to say its make or break?
Each match we play, I am responsible for the group and for Torreira also, today I think it is better [for Lucas] to leave the match.
The improved fitness may not show now, but it could help Arsenal down the road, when they face a busy stretch of games this fall between Europa League, Premier League and domestic cup competitions.
"It was disappointing to see the two goals go in because there was progress in the 90 minutes", said Emery.
"When you are 4-0 up you want to continue to be competitive and to score more goals not concede like today".More news: Gun activist who invented 3D printed firearm charged with teen sex assault
"It is a bit frustrating, but I keep calm and work very hard to improve. He had a big career and is still a very good goalkeeper - it is very good to work with him and for my development it is very good to have the competition with him".
Asked if he had been frustrated at being made to wait to make his debut, Leno replied: "Of course, because I came to the club to play every game".
"We are speaking before each match to take a mentality of "don't concede chances easily", he added. A victory in these situations is the best thing for us. "The Bundesliga is good but the Premier League is better so I will look forward to playing anytime in the Premier League".
"I want to give every player confidence", he said.More news: 'No-deal Brexit unless European Union softens position on border'
Emery said he is hopeful Torreira will be fit to face Everton in the Premier League on Sunday, and said the midfielder is improving with every game.