Febian Brandy opens the scoring
Febian Brandy scored his first goal in a Blades shirt to secure another morale-boosting victory for David Weir's team.
Very early into the game, the striker skilfully netted at the near post after controlling Darryl Westlake's right-wing cross.
The victory, attended by 691 Blades fans, also saw Lyle Taylor make his debut, playing the last 30 minutes after replacing Chris Porter.
Unitedites who made the trip to Field Mill saw Long in action for the first time this season, the teenage goalkeeper was given additional holiday time this summer after being part of England's U20s World Cup squad. Additionally, new signing Taylor was amongst the substitutes.
There was a nervous moments for Long within 15 seconds when he watched an effort from Howell drift past a post but the Blades were quickly on the offensive. Murphy had already tested the handling of Marriott before the initiative was seized on three minutes.
McDonald found Westlake on the right and his subsequent purposeful near post cross found BRANDY, who turned away from his marker to make space for a shot, which found the target between the legs of the Mansfield goalkeeper.
Marriott was then called upon to hold a Murphy free-kick and another Brandy shot, whilst the goalkeeper was credited with getting a touch to a Porter effort after the big striker had been expertly found by McDonald's crossfield pass.
Once again Marriott saved from Murphy as the one-sided half continued, whilst a deflection prevented Murphy getting on the scoresheet on 34 minutes and then Porter headed wide a Westlake cross.
Doyle shot at the goalkeeper but Mansfield's only serious forays into United's half was the first and last efforts of the half, the final one saw Williams around to cover to prevent Speight latching on to a Rhead pass.
The Blades were first to show in the second period and an impressive move almost brought a goal when Murphy's run enabled Brandy to lay-off for McDonald to curl just wide, whilst before the hour Taylor was introduced for his debut and Johns was given another chance to shine.
Mansfield, however, hit back with three efforts in four minutes midway through the half. Long tipped away a McGuire shot and Dyer's free-kick flew over the bar. A number of ricochets then presented an opportunity for Stevenson but Long adjusted well to parry away from the danger area.
Substitutes Johns and Taylor both had shots, the latter stinging the palms of Marriott, and although United were not as fluent as the first half, the visitors still held the upper hand.
Late on Long was off his line quickly to deny Dyer but the Blades comfortably held out to maintain the unbeaten pre-season run.
Stags: Marriott, Beevers, Black, Dempster, McCombe, Murtagh, Speight, Clucas, Daniel, Howell, Rhead.
Subs: Riley, McGuire, Dyer, Meikle, Hutchinson, Stevenson, Clements, Pilkington, Sutton, Tafazolli, Murray, Arnold.
Blades: Long, Westlake, Maguire, Collins, Williams, McGinn, Doyle (Whitehouse 81), McDonald, Brandy (McFadzean 76), Murphy (Johns 59), Porter (Taylor 59).
Unused: Howard, Whitehouse, Hill, McGinty.
Attendance: 1,912 (691 away fans)