A mistake from Watford goalkeeper Ben Forster allowed Pierre Emerick Aubameyang to deflect the ball in and a minute later Watford were down to ten men after Troy Deeney was sent off for throwing his hand into the face of Lucas Torreira.
The Hornets striker, who infamously claimed Arsenal 'lacked cojones' last season after Watford beat Arsenal 2-1, appeared to elbow Gunners midfielder Lucas Torreira as he made a cross-field pass.
The 30-year-old was instantly shown a red card by referee Craig Pawson, much to the amusement of the travelling Arsenal fans.
Speaking after that win in 2017, Deeney said Watford's physicality meant they overcame Arsene Wenger's side to win 2-1 in a Premier League match.
'There's a reason why they lost and it wasn't because of one penalty,' Deeney said. 'I'll have to watch what I say. It's (having) a bit of cojones, a bit of nuts. Whenever I play Arsenal, I'll go up and think, "Let me whack the first one and see who wants it".
Watford pressed for equalizer despite being reduced to ten men but the Gunners held on to claim all the three points to move to fourth place.
-Dailymail