Another Nick Blackman penalty was enough to ensure United's unbeaten run will continue into November.
The striker netted his eighth of the season when he converted a second half penalty after Lubomir Michalik clumsily brought down Chris Porter.
George Long was barely troubled as he recorded a third consecutive clean sheet, this time in front of the Sky cameras to leave Pompey without a win at Bramall Lane since 1955.
The teamsheets were handed in to the referee's room around an hour before kick-off and confirmed that Collins and Porter started for the Blades. Kitson missed out on the chance to face his former club with a hamstring problem, whilst McAllister dropped to the bench. For the visitors, ex Blades Harley, Williamson, McLeod and Ertl all started, but Howard was suspended.
Gaffer Wilson implemented a number of positional changes to allow Collins to slot back into his favoured central defensive role - Hill moved out to left-back and Williams into an advanced left-sided position. It appeared that the visitors were coming to terms with the changes when the Blades registered the first chance, with just 20 seconds gone, but goalkeeper Andersen saved with his legs after Blackman latched onto Porter's flick inside. An early Flynn corner also caused concern for the visitors.
Portsmouth's first effort, on 10 minutes, was extremely close - Buzsaky let fly from fully 35-yards and his shot had Long scampering before the ball cannoned back off the woodwork to McLeod, who was offside. Hill kicked away an Allan shot after a succession of corners and Collins cleared from Dickinson with McLeod ready to pounce.
In a frantic start the opportunities continued at a fair pace - Collins headed over a McMahon free-kick and then McLeod slammed into the Kop after McDonald's pass put Maguire under pressure. From a good move, Porter's flicked header was wide from McMahon's cross and Allan, for the visitors, was allowed to run 60 yards before sidefooting wide, Buzsaky then fired over a half-volley... all before the half hour mark.
Williamson - partnering Ertl in central midfield for the visitors - was warned by referee Russell for catching Flynn late and as half-time approached the chances slowed with the midfielders content to battle with each other.
When the second period kicked off, Pompey were quickly on the attack and Long had to paw away an effort by Dickinson following a corner and the intensity of the opening half hour had returned. The Blades had a spell of pressure in the Portsmouth half and on 55 minutes, following a neat turn, Maguire fired just over.
The officials were called upon to try and calm down a couple of minor skirmishes before the men in black were influential in United grabbing the lead on 66 minutes. From McDonald's ball down the right, Porter appeared to edge the ball away from Michalik, who caught the Blades striker right on the edge of the penalty area - one of the referee's assistants immediately indicated a a spot-kick and Mr Russell agreed. BLACKMAN again took responsibility for the penalty - slotting into the bottom corner, goalkeeper Andersen hardly moving from his central position.
McMahon and Harley were involved in a running battle in the second half and the right-back did brilliantly to prevent the ex United defender latching onto a Buzsaky pass. Portsmouth introduced a couple of offensive substitutes and, expectedly, saw more of the ball as the game entered the final ten minutes.
McDonald fired in a long-ranger, which was comfortable for Andersen, whilst boss Wilson introduced fresh legs in the shape of Miller and Cresswell as the clock ran down. Three minutes of added time was announced and comfortably seen off as three more points was added to the coffers.
Blades: Long, Maguire, Hill, Flynn, Doyle, Porter, Blackman (Miller 90), McDonald, Collins, McMahon, Williams (Cresswell 90).
Unused: Westlake, McAllister, Cofie, Ironside, Willis.
Pompey: Andersen, Dumbuya, Harley (Harris 74), Williamson, McLeod, Dickinson, Gyepes, Buzsaky, Ertl (Rodgers 78), Michalik, Allan.
Unused: Thompson, Walker, Compton, Eastwood, Webster.