A fantastic Jack Lester performance in second half made sure that Nottingham Forest where unbeaten in nine games.
Forest opened the scoring in 54th minute when Lester darted to beat Paddy Kenny after Ricardo Scimeca crossed.
Seven minutes later Forest went 2-0 up when Marlon Harewood set up Lester, fired home from 18 yards out.
Goal scorer turned provider when Jack Lester fed David Johnson on right hand side and Johnson's square ball met Marlon Harewood who finished from six yards out.
Before the game, Forest were 6th and United 5th, the win was well deserved as United gave a bad performance.
Before they broke the deadlock Forest looked to be in a frustrating day as Paddy Kenny pulled off a string of saves including tipping over a Gareth Williams shot over bar.
Lester was danger man in second half, but it was Johnson who was danger man in first. He was proving to be a thorn in United side and threatened to add to his 16 goals.
He cut in from the left to fire a shot just over the bar and then forced Kenny into an excellent save after prodding a close-range effort towards goal.
It was not all one-way traffic, however, and United were combative in midfield, but they were largely restricted to long-range efforts, with Michael Tonge and Carl Asaba testing Darren Ward in the Forest goal.
And when they threw men forward in the second half in a desperate attempt to get back into the game, they could not trouble Ward, even though Wayne Allison and Paul Peschisolido in particular peppered the Forest goal with shots.
There was to be no way back for the Blades, and Forest held on comfortably for a decisive victory.
Full-Time: Nottingham Forest 3-0 Sheffield United
Man of the Match: Not many contenders for this award after a bad performance, so I will give it Michael Tonge who was best player in United side.