Mulumbu, who scored the winning goal at the Liberty Stadium, has now called on fans to get behind the players for the remaining few weeks of the campaign.
"The best way to reply [to criticism] is on the pitch," he told the Express and Star. "I hope the fans stay with us.
"We have to work hard as a team to stay up and on Saturday we saw a team fight to stay in the Premier League. I'm really confident."
West Brom are back in action on Saturday with a trip to the KC Stadium to face Hull City.