The fourth-division club ceded the majority of possession, particularly in the second half, but held on in difficult weather conditions to earn a lucrative replay at Old Trafford.
The Red Devils, though pressing their advantage visibly in the final stages of the game, struggled to create clear-cut scoring opportunities.
Their biggest chance came in stoppage time when Adnan Januzaj crept through the massed ranks and forced goalkeeper Chris Dunn into an outstanding double save which kept the Us in it.
Radamel Falcao and James Wilson started up front for the visitors in the absence of the rested Wayne Rooney, while Adnan Januzaj was handed his first start since November.
