Said Benrahma headed a gilt-edged chance over in the first half and Vladimir Coufal hit a post in the second.

"I was pleased with the players, for long parts we controlled the game but we didn't have the difference up front," said Hammers boss Moyes.

"Neither did they, we gave them the goal. It was terrible defending, we were too easy to score against.

"We've done well but when you're really competing at the top you've got to be switched on all the time.

"We have to keep winning. I don't think we deserved to lose today so we need to get the next win under our belts as quickly as possible.

"I think because we've lost today defeat might be costly. but you never know in football.

"If we qualify for Europe I think it would be an incredible achievement, no matter which competition it is."

It was Everton's 11th away of the season, with only their poor home form preventing them from being in the mix for the top four themselves.

But the Europa League remains within reach after Calvert-Lewin's excellent strike.

The England forward latched onto Ben Godfrey's superb through-ball and out-paced Craig Dawson before firing low past Lukasz Fabianski into the bottom corner.

Everton boss Carlo Ancelotti said: "It was a vital victory, if we don't win here we are out of the fight for Europe.

"There was pressure on the game but we managed the game well. We played defensively at the top, really good, and were really dangerous on the counter-attack.

"The players knew it was vital. They also know Thursday against Aston Villa is vital. We have to be ready again to feel the game. The players understood, the attitude, spirit, concentration and motivation was very high.

"The goal Dominic scored is the goal of a top striker – cold in front of the goalkeeper."