Tommy Conway’s equaliser at London Stadium nine days earlier had set up this return tie and the 21-year-old striker was the Robins’ hero again as his early goal proved the difference.

West Ham, sixth in the Premier League, suffered further misery as Said Benrahma was sent off after 51 minutes for his reaction to a strong challenge from Joe Williams.

Although Moyes felt Darren England made the right decision to send off Benrahma, Hammer boss was unhappy over Williams’s tackle on the Algerian as well as one or two other incidents in the game, criticising the competition's inconsistency over VAR, which is currently not available for every match.

“It’s incredible they call it the best cup competition in the world. Yet one week you have VAR, one week you don’t," he said.

“I find it quite ridiculous they try to claim that, but it’s not level for every club.

“If we’re not having VAR we shouldn’t have it in the tournament at all. If we’re going to have it, then have it everywhere.”

West Ham was trailing to Tommy Conway’s third-minute goal when Benrahma was banished at the start of the second half.

“It made it much more difficult, that’s for sure,” Moyes said about trying to engineer a recovery.

“I’ve had a look at it and I don’t think we can have any complaints. I don’t think his reaction was correct. It was a sending-off.

“I wasn’t sure about the tackle on him. That might have been questionable. I thought in game-time it was a pretty hefty challenge.

“I’m not sure the referee moved in quick enough to deal with the first challenge, which allowed something else to happen. There was one on Danny Ings as well that was not the best either.”

On the defeat, Moyes added: “We should have won the game at London Stadium and done the job better.

“That’s what happens in the cup competitions – if you’re not quite on it, or maybe not at your best, you can find yourself knocked out.”

Bristol City, 14th in the EFL Championship, will again meet top-flight opposition in the fourth round should Nottingham Forest successfully negotiate its replay at Blackpool, and will host the victor of that tie.