Watford fans brought inflatable snakes to taunt Marco Silva but the surest way to torment their former manager lay in the club’s first victory at Everton. It was in their grasp until stoppage time, deservedly so, only for Lucas Digne to produce an antidote for Silva and Everton’s self-inflicted suffering.

Everton’s form has plummeted since they handed Liverpool victory in the 96th minute of the recent Merseyside derby. This time the 96th minute brought relief as Digne swept an exquisite free-kick into Ben Foster’s top corner following a careless handball by Christian Kabasele. Relief was fleeting as far as the Everton manager was concerned. His team led through Richarlison, the man who followed him from Vicarage Road to Goodison Park in the summer for £40m, and were punished for two lapses in concentration that produced an own goal from Seamus Coleman, plus what seemed an emphatic winner from Abdoulaye Doucouré.

Gylfi Sigurdsson also failed to convert from the penalty spot before the France full-back Digne came to the rescue with his first goal in English football. Everton’s performance, however, in keeping with last week’s home draw against Newcastle, gave Silva cause for concern.

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“Forget the derby, it is already past,” the Everton manager reacted. “That game is finished and we had to prove our quality in the next games.” They did not. “I agree with you,” he added. “We could not put our quality on the pitch in the second half. We gave them the chance to play long balls to Troy Deeney and prepare for second balls and we lost completely our focus and conceded the two goals. We gave them the chance to change the score.”

Javi Gracia was also left aggrieved, although the Watford manager’s annoyance centred on the referee, Kevin Friend, and not his players’ efforts to record a first win in six matches. Theo Walcott was clearly offside in the buildup to Richarlison’s opener but the goal was allowed to stand despite vociferous protests from the visitors. “I prefer not to say anything about the referees,” Gracia said. “But it was offside. If VAR was ready today the result would have been different. I’m very proud of my players.”

Richarlison scored five goals in his first 13 outings for Watford last season but none in the 28 games that followed or under Gracia. “At the end I told him that was the first goal I saw him score because he didn’t get one for me!” he said. The Brazil international claimed his eighth of the season when sweeping the hosts into an early, polished yet controversial lead.

There was no disputing the quality of the move that put Everton ahead. Walcott, making his 300th Premier League appearance, Coleman and André Gomes combined to breach the visitors’ defence. The Portugal international exchanged touches with Walcott before delivering an inch-perfect ball for Richarlison to convert at close range. But Walcott was offside when he received Gomes’s pass. Watford, their dispute over an alleged “unwarranted approach” for Silva unresolved, had another grievance with Everton.

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The hosts were initially bright in attack with Bernard and Sigurdsson bringing finesse and vision. The pair almost combined to create a second for Richarlison but Craig Cathcart made a crucial intervention. The defender also denied Sigurdsson, and Yerry Mina was booked for deliberate handball from Sigurdsson’s inviting cross. Mina flirted with a second yellow when he took Isaac Success and the ball as the forward broke in search of an equaliser. Enough of the ball in Friend’s view, to the obvious disgust of Success and Gracia. He would find consolation in his team’s dominant start to the second half.

The visitors’ strength, pace and movement – combined with a careless and chaotic restart by the hosts – turned the contest in their favour. Silva raged at his players from the sidelines but the lead evaporated before the Everton manager could implement change. Roberto Pereyra, Doucouré and Deeney went close before the equaliser arrived fortuitously but not without merit. A slip by Digne invited the former Evertonian Gerard Deulofeu to release Kiko Femenia down the left. His first-time cross was steered on to a post by Pereyra but, just as Watford thought their luck was out, the rebound struck Coleman on the thigh and rolled into an empty net.

Watford were ahead two minutes later thanks to another raid down their right. As Everton dawdled over a free-kick Gracia’s team reacted sharply with Femenia playing Pereyra into space. The Argentinian delivered a deep cross to the back post where Doucouré rose above Coleman and sent a textbook header past Pickford. Chaos continued when Kabasele needlessly fouled Mina in the area but Sigurdsson’s spot-kick was saved by the trailing leg of Ben Foster. Victory beckoned but then Kabasele erred again. Up stepped Digne and down went the snakes.