United climbed up to the second position above Leicester, but now they are seven points behind Manchester City’s champions, who still have a game in hand.
After just 83 seconds, the Baggies took a shock lead when on-loan striker Mbaye Diagne out-muscled Victor Lindelof to head in from Conor Gallagher’s cross.
United found it tough to make inroads in the grim opening period before Fernandes hooked Luke Shaw’s cross to the upper corner with his less powerful left foot.
Visitors improved in the second half, Mason Greenwood challenged Sam Johnstone with a low shot, and Scott McTominay saw his follow-up cleared the line.
With time running out, skipper Harry Maguire jumped to deliver his header to the top corner, but Johnstone tilted the effort to deny United the injury-time winner.
Sam Allardyce’s side may have taken it late in the day, but Diagne hit the crossbar from six yards to six.
Though they claimed a draw, West Brom remains in deep trouble at the wrong end of the table, second from bottom and 12 points from safety.