The Stags, fielding eight players aged 22 or under, tore into in-form Hereford from the kick-off and might have had a hatful of goals.
Ironically it was Stuart Fleetwood, Hereford's recalled striker, who created the first chance, racing 20 yards and curling a shot towards the top corner which the diving Jason White did well to hold.
But from then the home side dominated and the Bulls failed to create another chance until the game was lost as early as the 49th minute when Mansfield took a three-goal lead.
Full-back Alan Sheehan, making his debut on loan from Leicester, drilled a low 20 yard effort narrowly wide in the eighth minute after a neat one-two with Richie Barker as the Stags took control.
Then Simon Brown, put clear inside the area by one of several early clever Michael Boulding passes, crossed low inside the six-yard area where Boulding just failed to touch in at the far post.
However, the Stags finally found the breakthrough in the 19th minute courtesy of a Hereford gift.
Martyn Giles' diving challenge deflected Barker's 12-yard drive on to the bar after a good through ball from Jonathon D'Laryea.
But as the ball dropped back into the six-yard area, Tamika Mkandawire inexplicably headed the ball into his own net as the central defender and keeper Scott Tynan got into a tangle.
On the half hour Brown should have doubled the Stags' lead, but after bursting through on to another excellent D'Laryea pass he poked wide past the advancing Tynan.
Brown, injured in the resulting clash with the keeper, recovered enough to create the deserved second in the 36th minute, racing clear on to Stephen Dawson's pass and crossing to the near post where the sliding Barker bundled in.
The tricky wingman was then immediately replaced, but there was no let up in the non-stop home attacks.
Hereford manager Graham Turner switched from 4-4-2 to 5-4-1 at half-time in a bid to stem the flow, but Brown's replacement Danny Reet made it 3-0 four minutes into the second half by stooping to head in Matt Hamshaw's deflected cross.
Substitute Alan Connell gave Hereford hope of an unlikely fight back in the 68th minute by bringing down a corner and poking a fine finish into the top corner.
But those hopes were dashed just four minutes later when Trent McClenahan tangled with Boulding as he tried to reach a Hamshaw cross and Barker thumped in the resulting penalty.