First half goals from Morgan Gibbs-White, Iliman Ndiaye and Sander Berge put the Blades in cruise control inside the opening 30 minutes before Enda Stevens got in on the action after the break.
The win means United will play Nottingham Forest in the play-off semi-final.
Steve Cooper’s side drew 1-1 against Hull City this afternoon.
The first leg will take place at Bramall Lane next Saturday with the return fixture on Tuesday 17 May.
Here’s our player ratings after a brilliant afternoon.
9. John Fleck - 7
A steady showing in the middle of the park helped United to a very comfortable win. Photo: David Klein
10. Iliman Ndiaye - 9
Like his partner, grabbed a goal and an assist. Managing the high-pressure task of leading Sheffield United's attack with distinction. Photo: Danny Lawson
11. Morgan Gibbs-White - 9
Goalscorer and creator once again. Simply brilliant in the first period and his partnership with Ndiaye is a joy to behold. Photo: Simon Bellis
12. Sander Berge - 9
One third of a deadly attacking trio who terrorised Fulham in the opening 30 minutes. Helped himself to a goal and an assist. Arguably the best player on the park over 90 minutes. Photo: Danny Lawson