Troy Deeney was sent off as Arsenal beat Watford to record only their sixth Premier League away win of the season and move back into the top four.
Hornets captain Deeney was shown a straight red by referee Craig Pawson after catching midfielder Lucas Torreira with a forearm after 11 minutes.
Deeney was left incensed by the decision while his head coach, Javi Gracia, was also seemingly unhappy with the sending off.
It was part of a chaotic two minutes for Watford, who 60 seconds before that conceded the only goal of the game when Pierre-Emerick Aubameyang charged down goalkeeper Ben Foster’s clearance.
Other than that, Watford dominated large parts of the game and they twice hit the woodwork on a night where they will feel aggrieved they didn’t at least secure a draw.
Arsenal, on the other hand, will be thankful to have recorded their first clean sheet away from home in the Premier League this season as the three points means they move back into fourth place.
In preparation for their trip to Napoli on Thursday for the second-leg of their Europa League quarter-final, Unai Emery made six changes for this clash with Watford.
That included a first start since May for defender Konstantinos Mavropanos, who looked shaky from the off as within 10 seconds he missed a simple header back to goalkeeper Bernd Leno.
It was all part of a nervy start from Arsenal, who were being pressed and harried by a Watford side full of confidence after their FA Cup semi-final win against Wolves last time out.
However then, in the space of just two minutes, Watford’s evening unravelled as they first conceded and then Deeney was sent off.
Arsenal’s only goal, which came after 10 minutes, came in fortuitous fashion as Foster dallied on the ball and allowed Aubameyang to block his clearance into the net.
As if that wasn’t bad enough, only a minute later striker Deeney was shown a red card by referee Pawson after catching midfielder Torreira with his forearm.
The assumption was Arsenal would go on and dominate from there, but instead it was Watford who took charge. Craig Cathcart struck the post from inside the box, while Leno had to be at full stretch to deny Etienne Capoue’s 20-yard free-kick.
The Gunners steadied the ship through to half-time, but Watford went in at the break wondering how they were trailing.
Looking to change things, Emery introduced Mesut Ozil for the second-half as Torreira made way and Aaron Ramsey dropped into a deeper role.
The German’s introduction certainly seemed to calm Arsenal down and they began to control the tempo of the game.
Indeed they should have doubled their lead 11 minutes into the second-half when Alex Iwobi’s dinked cross found Henrikh Mkhitaryan, but Foster made a good save to deny him from close range.
At the other end, Watford were going all out for to score as the game ticked into the final 30 minutes and left-back Adam Masina rattled the crossbar with a brilliant strike from 30 yards.
Gray then went close with 10 minutes to go as he rounded Leno, only for substitute Ainsley Maitland-Niles to deny him with a superb covering tackle.
However, Arsenal held on to secure a vital three points which keeps them in the driving seat to finish in the top four and return to the Champions League next season.