Arsène Wenger blamed a “scandalous” penalty decision and his own team’s lack of killer instinct for a damaging 2-1 defeat at Watford. Arsenal looked on course for victory thanks to Per Mertesacker’s first Premier League goal for almost four years but ended up leaving empty-handed after Troy Deeney equalised from the spot and Tom Cleverley struck a winning goal in stoppage time.

Neil Swarbrick awarded the second-half penalty in the belief that Richarlison had been fouled by Héctor Bellerín but Wenger insisted any contact had been negligible. “The decision on the penalty is a bit ridiculous and then we panicked a bit for their second goal and in the end we stand with a defeat,” the Arsenal manager said.

“It is a scandalous decision, but what can we do about it? Nothing. We can talk and talk and talk. At the end of the day they scored. It was not a penalty, it was a creation of the referee. The decision is wrong and that’s it. And it came at an absolutely important time for them. No penalty, no goal.”

Marco Silva, Watford’s manager, suggested that he could understand Arsenal’s view but also said that Swarbrick had grounds to point to the spot. Silva stressed that Richarlison was not guilty of simulation. “It is not an easy decision,” he said. “But he did not dive. He is always fair. It is very important to understand what a dive is. This was 50-50. There was short contact. After the match at West Brom I called for skilful players to be given more protection. Richarlison, a young boy of 20, is the most fouled player in the Premier League. All the greatest players in the world attract fouls.”

Wenger did not exaggerate the effect of the penalty. He admitted his team were at fault, too. “[The penalty] was not the only major factor in the game,” he added. “With a bit more killing instinct in front of goal, we should have won the game. That’s where we’re guilty.

“We played very well in the first half but I’m not so happy with the second. Our level dropped. We missed many chances. The number two and number three goals should have been scored. And after the 1-1 there was no need to panic. For their second goal, we can only look at ourselves.”

The result lifted Watford into fourth but Silva said: “We have one goal, we want to remain as a Premier League club.”