The United striker stabbed the ball over the line in the fifth minute of injury time to dent Leicester's hopes of the championship.
United were in trouble in the fourth minute when a sparkling three-man move sliced through the United back four. Paul Dickov picked out Trevor Benjamin who appeared to elbow Peter Ndlovu before crossing from the left for Brian Deane to hit a crisp volley beyond Paddy Kenny into the far corner.
United were level after 15 minutes. Michael Tonge did the hard work cutting in from the left and squeezing past Matt Elliott before picking out Carl Asaba who turned quickly to squeeze the ball past Ian Walker at the near post.
Peter Ndlovu tried his luck from long range but fired wildly over the bar before drilling in a centre from the right , the ball flying across the face of the Leicester goal with Dean Windass just failing to connect as the Sheffield side grabbed the initiative.
The Blades' midfielder Michael Brown broke clear on 28 minutes after hard work by Tonge, sweeping past one tackle before letting fly with a left-foot shot from the edge of the area, the ball flying wide of the far post.
Deane squandered a half-chance hammering the ball into ground and over the top and seconds before the interval midfielder James Scowcroft caught Kenny napping with a shot on the turn, beating the United keeper only for the ball to cannon off the foot of the post.
The woodwork saved Leicester four minutes after the restart. Windass found Asaba, the big striker picked out Ndlovu with a downward header and the ex Birmingham midfielder fired an eye caching volley from 18 yards, the ball hitting Walker's right hand post.
Dickov slammed a free-kick straight at the United keeper before Leicester were reduced to ten men in the 55th minute, midfielder Callum Davidson ordered off after upending Brown, his second booking of the game.
Brown went close twice before Shaun Murphy headed an Ndlovu cross into the goal mouth and Asaba added the finishing touch.