Just when Arsenal had most to gain from winning, with all the teams around them dropping points, and just when they were gifted what looked like a walkover fixture, against Watford at home, they produced their worst performance of the season.

Arsenal were dismal, utterly absent from the game and conceded two early preventable goals from which they never recovered. It took them until the start of the second half to wake up, and although they improved, they had left themselves too much to do.

This was not the heaviest defeat of Arsenal’s season it but it is by far the worst. It was so unexpected, so avoidable and so self-inflicted. This was against Watford, the team who had won just twice away from home all season, against Middlesbrough and West Ham United. Watford, who had won just one of their last nine games, and that against Burton Albion. Arsenal, it is easy to forget now, had won five out of six before this one and were predictably stable, certainly at home.

With all due respect to Watford, who were very good, home teams win these games by doing the basics. And on this night, under these sheets of rain, that is what Arsenal completely failed to do.

Former Tottenham player Kaboul scored against the Gunners (Getty)

In the first game of Arsene Wenger’s touchline ban, Arsenal played with the easy freedom of schoolboys enjoying themselves while their teacher was away. Tonight it all went too far, and they looked like pupils revelling in the fact that there was no-one there to enforce standards, no-one to keep them in line or make them do the basics. The first 20 minutes of play were an embarrassment for Arsenal, with their players barely winning a single 50-50 and allowing Watford to walk straight through them.

When Arsenal players did make a challenge, they gave away needless free-kicks, and it only took 10 minutes for Watford to punish them. Tom Cleverley tapped the ball to Younes Kaboul, who smacked it hard and low. Aaron Ramsey turned half-heartedly into it, the ball flew off his thigh and into the bottom corner.

That was bad enough and less than three minutes later Arsenal conceded an even worse goal. Etienne Capoue won the ball in midfield, drove past Aaron Ramsey, shuffled away from Francis Coquelin and then from Shkodran Mustafi. Petr Cech at least provided some resistance, saving Capoue’s shot, but the rebound just flew away to Deeney who put it in.

The closest Arsenal got to scoring in the first half was when Nacho Monreal burst into the penalty area from the left after 25 minutes. He threw himself to the ground in the vicinity of Sebastian Prodl and was booked for diving.

Watford took the lead far too easily (Getty)

Despite their caution, Watford still managed to be more dangerous than Arsenal. Cech had to make two more saves before half-time, from Prodl’s header and Daryl Janmaat’s shot. Heurelho Gomes, to the surprise of everyone in the stadium, could jog in for half-time without having had to make one single save.

Arsenal knew they needed to change and Theo Walcott came on for Olivier Giroud. Alex Iwobi moved to the left, Alexis Sanchez back up front and Arsenal had their edge and speed back. Walcott, fresh from a hat-trick on Saturday, whistled one shot just wide then forced Gomes to save with another.

Iwobi, moved onto the left, was the best player on the pitch, skipping away from yellow shirts every time he burst through the rain. He found Oxlade-Chamberlain, received a back-heel in return and forced a brilliant save from Gomes.

Alex Iwobi pulled one back for Arsenal (Getty)

With Iwobi’s next attack he scored. Sanchez broke away down the right, turning and clipping a cross up to the far post. Iwobi’s leaping volley sent the ball back between defenders and into the net.

That was one third of the job for Arsenal, and in truth they never really got close to completing their comeback. Lucas Perez came on for Coquelin, a change that made sense at the time, but one that unbalanced a team that had just started to play well. Arsenal lost their width, cramped themselves and found that the only shots they had were from distance. Monreal whistled one wide from distance, Perez thundered one against the bar but a second goal never looked like coming, never mind a third.

Watford worked hard, took their chances and deserved to win, but this was a night when Arsenal beat themselves. And it was Watford at home, not Chelsea away, which is their game on Saturday. They know they will have to play 10 times better than this, but even if they do it could still be too late.

Arsenal (4-2-3-1) Cech; Gabriel, Mustafi, Koscielny, Monreal; Ramsey (Oxlade-Chamberlain, 20), Coquelin; Iwobi, Ozil, Sanchez; Giroud