Mulumbu relishing an extended run with Dorrans in the middle of the park.
"I used to play a lot with him in the Championship and we had a good partnership," he told the Albion website.
"He's a very good, skilful footballer and it was easy for me to play next to him today. We have a good understanding and he makes it easy for me to find a pass. I think it was really good for him to score today.
"He hasn't played a lot of games this year and it was important for his confidence that he scored.
"I hope now he will play more games.
"And I hope now we can finish in the top half of the table as we no longer have to look over our shoulders."