BEN FOSTER gifted Arsenal a way back into the top four with a horror blunder.
The Watford keeper failed to notice a prowling Pierre-Emerick Aubameyang as he went to clear the ball inside his six-yard box on 11 minutes.
The Arsenal striker pounced to sending Foster’s kick rebounding into the net, leaving the keeper with his hands on his head.
And Watford’s woe was compounded when, 37 seconds after the restart, Hornets skipper Troy Deeney was red-carded for a forearm smash on Lucas Torreira.
Deeney could have few complaints after allowing his enthusiasm to get the better of him and leaving his team-mates in the lurch.
Arsenal boss Unai Emery had handed a first start of the season to Konstantinos Mavropanos, 21, to deal with the physical threat of Deeney.
But the young centre-half did not even have a chance to get a challenge in before his opponent had gone.
Watford’s panto villain of a captain has always relished the opportunity to test Arsenal’s bravery.
When Granit Xhaka went down with barely a touch from Adam Masina, he was straight into the midfielder’s ear to urge him to stay on his feet.
But being pumped up is one thing. Running out of control is a different matter.
So he was always pushing his luck when he swung an arm towards Torreira as they competed for possession.
Because Deeney had such a height advantage over the diminutive Arsenal midfielder, he was perhaps unfortunate to catch his opponent in the face.
But that was not the way linesman Richard West saw it as he reported the incident to referee Craig Pawson.
Deeney was adamant that he had accidentally caught Torreira, but Pawson was having none of it as he fished the red card from his pocket.
And he was still arguing his innocence to the Arsenal bench as he reluctantly made his way from the pitch.
His departure left the FA Cup finalists facing a very long evening as they struggled to cope with the numerical disadvantage.
They were already a goal down by that time after Pierre-Emerick Aubameyang had cashed in on another mental aberration from Ben Foster.
The Watford keeper seemed to be in complete control when he shaped up to take Daryl Janmaat’s 8th minute backpass.
But he was undone by a shocking first touch which allowed Pierre-Emerick Aubameyang to charge down Foster’s panicked attempted clearance for his 23rd goal of the season.
It was a horrIfic error by the normally reliable Foster which was compounded four minutes later by Deeney’s ill discipline.
The red card incensed the Vicarage Road crowd and that sense of injustice appeared to spread to the Watford players as they looked to settle a few scores.
Torreira was clattered by Abdoulaye Doucoure and Laurent Koscuielny was not impressed when Richard Hughes left a foot in on him.
Etienne Capoue was eventually booked for another meaty challenge on Henrikh Mkhitaryan ro leave Arsenal fearing for their well-being ahead of Thursday’s Europa League return in Naples.
The visitors should have been out of sight by then but Aubameyang’s shot was deflected just wide by Craig Cathcart before Alex Iwobi was denied by a sharp Foster save.
Yet even with their extra man Arsenal were making hard work of securing the victory required to move above Manchester United and Chelsea in the table.
Capoue’s 32nd minute free-kick drew the save of the night from Bernd Leno and Adam Masina struck the bar from 25 yards midway through the second-half.
Arsenal had already withdrawn Torreira for his own safety by then but even the introduction of Mesut Ozil as a half-time sub could not produce the second goal they needed to crush Watford’s spirit.
Mkhitaryan almost made the breakthrough from Iwobi’s 57th minute cross but it was Watford who finished the game the stronger.
Andre Gray thought he had grabbed the equaliser his team’s efforts deserved when he beat Leno to Isaac Success’ 81th minute but his shot was charged down on the line by Ainsley Maitland-Niles.
It was just about enough to preserve Arsenal’s first away clean sheet in the League all season.
But Emery knows that even a two-goal lead will not be enough against Napoli if his team cannot do better than this.