It looked as if the Blades, who were beaten in the Capital One Cup semi-final by Tottenham last week, would continue their love affair with the cup competitions as they led through Jamie Murphy’s first-half opener.
But they were second best throughout and Preston responded in style after the break as Paul Gallagher netted either side of Paul Huntington’s header to clinch a meeting with Louis van Gaal’s side, who saw off Cambridge 3-0 in their own replay on Tuesday night.
It was thoroughly deserved for the visitors, who bossed matters from the off and should have been in front after 12 minutes when a defensive lapse from Chris Basham sent Kevin Davies clear but, with time and space, the veteran striker could only hit the post.
There were further chances for Simon Grayson’s men and home goalkeeper Mark Howard made a hat-trick of saves, the best a superb low stop to keep out Tom Clarke’s back-post header.
And it was against the run of play when the hosts, who reached the last four of this competition last season, stole into a 38th-minute lead as Murphy cut inside and his low shot went through keeper Thorsten Stuckmann’s grasp.
It was an open start to the second half, with both sides threatening, but Preston wrapped up the tie with a 10-minute three-goal salvo.
Gallagher’s moment of brilliance brought the sides level after 63 minutes as the on-loan Leicester man whipped a stunning 18-yard free kick into the top corner, and Huntington’s header from Scott Laird’s corner six minutes later put the visitors ahead.
The game was made safe when Gallagher netted from the spot following Jay McEveley’s foul on Chris Humphrey, and United had no response as their impressive cup exploits ended for another season.