Darren Bent came off the bench to cancel out Shane Long's opener for the Baggies.
He said: "I think it was harsh going behind, especially after the first half.
"The goalkeeper (Ben Foster) has made two world-class saves and when you go behind, especially in a derby, it puts you on the back foot.
"I thought the response was great, especially after playing 120 minutes on Tuesday. It was a big, big ask but the response was excellent."