United's title bid suffered a blip at The Hawthorns as the Reserves failed to score for a second successive game.
Nicky Shorey's first-half opener proved decisive and, despite an improved display after the break, the Reds were unable to find a way past home keeper Luke Daniels. After Jesse Lingard had a couple of early efforts off target, Albion took the lead when a quickly-taken corner allowed Shorey to cut inside and bury a right-footed curler past Ben Amos.
Only a top-class save by Amos prevented Adil Nabi from extending the lead soon afterwards and Albion were decent value for their first-half lead. Wesley Atkinson screwed a shot wide for the hosts while Daniels didn't have to make a save until the 34th minute when he stopped a tame Lingard effort.
Will Keane was constantly outnumbered by defenders in attack but, after Ezekiel Fryers popped a drive the wrong side of the far post, the England Under-21 international muscled his way through to round Daniels, only to see Cameron Gayle make a goalline clearance.
Warren Joyce's half-time team-talk had the desired effect as, with Lingard moving more central, the pressure was applied right from the referee's whistle. Lingard forced a fine save out of Daniels following good work from Will Keane and then pulled the ball agonisingly across the six-yard box with no team-mate on hand to apply the finishing touch.
A brilliant solo run by Will Keane was not matched by the shot, as Daniels saved comfortably, but the home keeper had to be at his best to beat out a Davide Petrucci shot from close range.
Joyce handed teenagers James Wilson and Mats Daehli their debuts at this level and, although Lingard worked Daniels again, Albion weathered the storm.
Shorey shovelled over and Amos saved from Liam O'Neil and Graeme Dorrans before the Reds came on