Arsenal's goal from Pierre-Emerick Aubameyang came as a result of the Gabon worldwide closing down a slow clearance from Watford goalkeeper Ben Foster and the Arsenal manager admitted that it was a tactic to close down the former Manchester United man.
Just a minute later, Watford captain Deeney was sent off for throwing his forearm into the face of Arsenal midfielder Lucas Torreira in a late challenge.
It will also be a huge concern for the Arsenal boss that his side have been poor on the road this season and they lost both away legs in the previous knockout rounds against BATE Borisov and Rennes.
"We are showing we are competitive and have a good mentality", he added.
"We are glad that we did not concede a goal".
'We are starting the game by attacking when we have the ball and have the space to run but defend when we need as well.
"When it is 1-0 they have chances, their moments". It's more hard for them. "But above all the three points are more important".
"Courage, we had little in London in the first half, there was intelligence in the second half, we must put the heart tomorrow with a high dose of intensity". Our analysis will give us confidence.
The home side missed their best opportunity in the 80th minute when Arsenal substitute Ainsley Maitland-Niles slid in to block Andre Gray's goal-bound effort after the Watford forward rounded Leno. "They want to do something important", said Emery.
"I only have one feeling". We did everything to win.
Let us know in the comments. It was a good performance.
"Everyone knows me and Arsenal don't get on too well", he said. In my opinion it is a yellow card but never a red. I don't understand why the referee did it. We have players who have played here before.
"We tried to keep being compact in the middle with two lines of four and Andre up front. We were the better team, pushing for it. Arsenal were happy to hit us on the counter", Foster told Sky Sports.
"Ben Foster and all the players deserve credit". The atmosphere will be very good.