Moyes felt that his side got what they deserved on Saturday.
"Disappointing performance, disappointing result. We never really got upto speed," Moyes said.
"We had a few chances, but West Brom held their shape, defended well and deservedly won the game."
Adnan Januzaj replaced Shinji Kagawa at half-time for United.
"I just tried to find another way, change things from the first-half," Moyes explained.
"I thought young Adnan came on and did really well."
"I have a strong team here at United, some good players, so I am in no doubt we will put it right.
"We will just go out and try and win the next one."