Second-half goals from Tony Craig and Marc Laird completed a double for the Lions over the Bulls and ended Hereford's recent mini revival.
Millwall had much the better of the first period with Izale McLeod providing plenty of food for thought for Bulls centre-backs Karl Broadhurst and Josh Gowling.
It was Hereford, though, who came closest in the early stages when Andy Williams turned neatly inside the area but saw his shot hit the outside of a post and go behind.
Craig Samson, in the Hereford goal, was by far the busier of the two keepers and he did well to turn away a fierce drive from Lewis Grabban for a corner.
Samson was found wanting only once in a busy opening period, missing his punch from a Dave Martin corner. Steve Guinan came to his rescue with a clearance.
Hereford were able to venture forward only rarely but, from one of their raids, Paul Robinson was yellow-carded for hacking down Matt Done.
In a lively opening to the second period, Hereford's Toumani Diagouraga had a shot cleared off the line by Andy Frampton.
Guinan then saw a couple of straightforward efforts saved by David Forde as Hereford strove to extend their recent good run.
After Millwall had won their seventh corner of the evening Martin delivered a deep cross to the far post and, with Samson failing to collect, Craig's header took a ricochet into the net from ten yards.
In injury time Samson could only parry a fierce drive from the impressive Grabban and Laird stooped to head into the unguarded net.