After scoring a brace against Blackburn Rovers in the Lancashire Cup just before Christmas, the Senegalese striker gave Warren Joyce's side the perfect start, latching onto Davide Petrucci's measured pass in the eighth minute to round Matt Glennon and tap home.
It was largely one-way traffic with Petrucci firing wide, Diouf sending a spectacular effort off target and Jesse Lingard going close on a couple of occasions while Ben Say and Sean McConville survived a couple of near misses in terms of putting through their own net.
After Diouf had a goal chalked off for offside in the second half, the former Molde hitman linked up superbly with Lingard and the midfielder's fierce drive cannoned off the inside of Glennon's left-hand post when the move deserved a goal. Diouf struck the other upright two minutes later, from another Petrucci through ball, and Lingard was frustrated by firing wide and then being subjected to a late offside call after beating Glennon.
The visiting keeper made telling saves to thwart Diouf and Larnell Cole but could do little with substitute Michael Keane's spectacular drive in the final minute that again rattled the woodwork, following a perfectly-timed pass by Lingard.
United: Amos, Vermijl, Fryers (M. Keane 46), Fornasier, Thorpe, Brown (Massacci, 59), Cole, Norwood, Diouf, Petrucci, Lingard. Subs not used: Coll, Rafael Leao, Giverin.