A late Ched Evans goal gave United a pre-season boost on the Algarve.
The Welsh striker scored with four minutes to go at the Estadio da Bela Vista in Parchal against Portuguese top flight outfit Maritimo. An estimated 850 United fans were in attendance.
It was a deserved victory as United bossed the first half. Lee Evans failed to chip the goalkeeper when in the clear and Clarke sidefooted wide after Fleck's deep cross in the early exchanges.
An unmarked Lafferty headed wide a back post cross by Holmes, who moments later nicked the ball on the edge of the box but saw his effort drift just wide.
There was one more miss before the break with Clarke firing across goal and wide after United won back possession deep in Maritimo's half.
After a number of changes at the break, Maritimo went close on 47 minutes but Henderson made a comfortable save.
Lavery was denied by a near post save after Basham and Freeman linked up on the right and during the second half there were a couple of yellow cards after some meaty challenges.
Maritimo went close courtesy of an indirect free-kick in the box after Henderson picked up a backpass, but United's winner arrived on 86 minutes. Freeman's deep cross saw Stevens head back into the danger area and EVANS steered home from close range.
Blades: Henderson, Baldock (Freeman 45), Basham, Stearman, O'Connell, Lafferty (Stevens 45), L Evans (Leonard 45), Fleck (Duffy), Holmes (Slater 54), Clarke (Lavery 45), Sharp (C Evans).
Unused: Eastwood, Norrington-Davies.