Arsenal took the lead after 10 minutes when Ben Foster’s clearance rebounded off Pierre-Emerick Aubameyang into the net, and one minute later Troy Deeney was given a straight red card after he was deemed to have elbowed Lucas Torreira.
While Emery was thrilled to take home all three points, he was disappointed his side failed to score a second goal.
“Our position in the table is very important,” he said. “It is in our hands, to take the top four.
“We were working to push the goalkeeper when he wanted to play like he was playing. It’s a very good action from Auba.
“I think we can control the match better, and I think it was very important in this position with one player more, to break their lines and to attack the last third better.
“But I think it’s very positive to have all three points.”
Much was made of Watford’s aggressive style of play in the build-up, following comments made by Deeney last year that challenged Arsenal’s courage and bravery.
Emery praised Watford’s approach and ability to adapt to losing Deeney early on.
“They are very aggressive, they push a lot with their supporters, and we know that,” he added. “They play it, pushing a lot, with one player less in their team they worked it very well and they work at pushing us.”