Federico Macheda bagged the second-half winner for Warren Joyce's side, after Will Keane's opener had been cancelled out by Dale's Neal Trotman.
The Reds fielded four Italians in the XI and had to battle for supremacy, although Keane fired one chance wide following outstanding approach work by Paul Pogba in midfield and Davide Petrucci whistled a drive off target.
David Lucas saved from Macheda and Petrucci but was beaten six minutes before the interval. Macheda's thrust down the left forced a great stop out of Lucas and Keane converted the rebound at the second attempt with an improvised, scooped finish that illustrated his composure.
Tomasz Kuszczak kept the scores level by thwarting Reece Gray and Ahmad Benali but had no chance when Neal Trotman powered home a header from a Brian Barry-Murphy free-kick on the right. United were spurred to retaliate against impressive, combative opponents but Diouf lashed a left-footed shot over the top and Keane hooked a defence-splitting pass from the increasingly influential Petrucci wide.
After Diouf was unlucky with a flick from a Pogba free-kick, superb strength from Keane allowed Macheda to bag the winner as the Italian striker's shot spun off the hand of Lucas and rolled over the line. Diouf was too unselfish when played in by Pogba and Macheda saw another attempt scrambled behind by Lucas but United were unable to kill Dale off. And there was a late scare when Benali's trickery on the right led to substitute Ola Radbiu blazing over from close range.
United: Kuszczak; Massacci, Fornasier, Thorpe, Fryers; Pogba, James (Giverin, 46), Petrucci;