United's penultimate encounter of the league campaign ended in defeat on the road at Crewe.
Crewe goalkeeper Steve Phillips made a number of fine saves, which earned him the man of the match award, but striker Chuks Aneke scored the decisive goal early in the second half.
The defeat left United in sixth position in League One with a play-off position safely in the bag.
As promised, temporary boss Morgan freshened up United's team for the game - he made five changes with Westlake, Maguire, Forte, Robson and McFadzean, who made his full league debut, all starting. Flynn and Murphy dropped to the bench and there was no place for McMahon, Kitson and Hill.
The early formation was Robson supporting Porter from a central area, with Forte on the right and McFadzean on the left. At the back Higginbotham moved out to left-back to accommodate Maguire.
Wearing white shirts, the Blades made a positive start, although Forte blasted over the crossbar. On five minutes, from a Robson free-kick, Maguire's power header was pushed away by goalkeeper Phillips and after Forte chipped back into the danger area, Collins was crowded out by Mellor.
Forte shot wide after robbing Stewart and on 25 minutes McFadzean was given the first chance to use his pace down the left, his shot was parried and Phillips recovered to smother the rebound from Porter.
For Crewe, Moore's deflected effort was wide but Long was not troubled in the first half hour. At the other end, Robson's deliveries were causing problems for the home side and a long-range effort from McDonald was pushed away by Phillips on 32 minutes.
Before the break, the home side created a number of chances. Leitch-Smith's deflected shot was comfortable for Long and a header from Ellis was blocked. An Aneke shot was pushed away by Long and in the solitary minute of injury-time a free-kick from Davis flew over the crossbar.
At the start of the second half the Blades made a change, Murphy replacing Higginbotham with McFadzean dropping to left-back, but Crewe took the lead with their first chance of the half. Inman held possession on the right and laid off to ANEKE, who rolled the ball onto his right boot before curling into the corner of the net, beyond Long's left arm.
United's response was a 25-yard free-kick from Robson, which Phillips punched away, and Forte also fired wide. Collins picked up the game's first booking, presumably for speaking out of turn, whilst Morgan's second change was to replace Forte with Ironside, who shot wide within moments of coming on.
Chapell was the last change, replacing Robson, and although United were seeing a lot of the ball, most of the opportunities were falling to the home side with goalscorer Aneke going close on two more occasions.
In the final ten minutes Chapell fired into the side-netting and Porter was unable to get on the end of a Doyle cross which Phillips spilled, whilst just before three minutes of added time was announced, McDonald shot wide.
The injury-time period brought a great chance to equalise but Phillips again proved United's foe, turning Ironside's shot around the post.
Crewe: Phillips, Davis, Ellis, Leitch-Smith (Ray 88), Moore, Turton, Mellor, Osman, Aneke (Ellington 86), Inman, Stewart.
Unused: Tootle, Clayton, Garratt, West, Colclough.
Blades: Long, Westlake, Higginbotham (Murphy 45), Maguire, Doyle, Porter, McDonald, Collins, Forte (Ironside 65), Robson (Chapell 70), McFadzean.
Unused: Flynn, Whitehouse, Barry, Coyne.