The visiting Red Devils dominated possession in the opening 45 minutes, yet the hosts created the better chances – neither of them clear-cut however, as wasteful balls were played in the box while a number of shots from range failed to truly test David De Gea in the United goals.
The biggest talking point of the first half though was the sending off of Juan Mata: after needlessly closing down a West Brom free-kick to earn his first yellow card, the Spaniard recklessly went in for a challenge three minutes later to leave his side down to ten men after just 26 minutes played.
Despite being a man down, United started the second period on the front foot and with attacking intent, yet the one man disadvantage began to take it’s tool as the half wore on.
And midway through, on 66 minutes, United’s resistance finally crumbled as Sebastein Pcognoli cross from the left found Salomon Rondon who took a touch to control the ball before swishing it past De Gea for his eighth of the season to hand his side the lead.
And it was a lead the Baggies would not relinquish as they earned their first League victory over United in 32 years to lift them to 11th in the EPL table.
United, meanwhile, remain in sixth and out of the European spots, two behind fifth-placed West Ham and 13 off leaders Leicester City.
Earlier in the day, a late and controversial Christian Benteke penalty secured Liverpool an injury-time 2-1 win over Crystal Palace, Roberto Firmino cancelling out Joseph Ledley's opener, as the Reds remain seventh in the standings, with Palace in 15th.