Bit more of everything
Bilic's side returned to Old Trafford on Wednesday night with confidence after Sunday's 1-1 draw with Jose Mourinho's side in the league. However, they got off to the worst start with Zlatan Ibrahimovic opening the scoring just two minutes in.
The Hammers managed to get back in the game when former United starlet Ashley Fletcher equalised with his first goal in claret and blue.
But two goals from Anthony Martial and another from Ibrahimovic saw the Londoners crash out, and Bilic shared his frustration at his side's performance.
“We can’t have a slow start against them because they are very good when they are one up," Bilic told whufc.com. "They have those kind of players."
“After the slow start, we recovered and looked good but you can’t do the same," he stated. "They totally deserved it then after that. You just can’t have that kind of a start in a game like this."
“They are really good on the counter attacks and all that but that happened to us in the first half," the Croatian admitted. "Then we recovered and started to play after 25 minutes."
Bilic added: "They played with more energy and quality and a bit more passion.”
Bilic hopes injury not that bad
It got worse for the Hammers, with injuries to both Aaron Cresswell and Michail Antonio.
The club have been dreadfully unlucky with injuries this season but Bilic has said that he is hopeful that the pair will return for Saturday's clash with Arsenal.
“Cresswell’s injury doesn’t look that bad," he said. "His groin felt very tight and hopefully it’s just fatigue from Sunday. With Antonio, hopefully it’s the same but we don’t know yet."
“We have a tough game on Saturday and we have a couple of players who came off injured," the coach stated. "But we wanted to preserve players for then and Dimitri Payet also."
Bilic concluded: “It is unbelievable that when we get a couple of injuries like the ones we got today [after them all this season] and it’s very tough for us now.”
West Ham United will take on Arsenal at the London Stadium on Saturday, December 3 with kick-off at 5:30 GMT.