James Beattie took full advantage of the Foxes frailties, and in complete style, completing a hat-trick inside seven minutes to leave Holloways side stunned.
Leicester held on in the second half to deny a Utd goal fest, with Henderson making a series of impressive stops to spare the Foxes further embarassment.
There will be complaints about Kisnorbos sending off which lead to the opening goal.
However, there can be no complaints about the result, Sheffield United were the better team on the day and deserved the win.
The result sees the Foxes fall to 20th in the Championship table one point clear of FA Cup semi-finalists Barnsley who have two games in hand.
Meanwhile, Sheffield Wednesday were only able to pick up a single point at Scunthorpe and so the Owls upcoming visit to the Walkers Stadium may decide who occupies the final relegation spot on the last day of the season.