Kevin Davies fired in a late winner to help Bolton's European push and leave Sheffield United looking over their shoulders at the bottom three.
Davies broke Blades' resistance and Kenny's heart
Davies' low shot from 20 yards inflicted a seventh successive away defeat on the Blades for whom keeper Paddy Kenny was in inspired form.
Kenny pulled off stunning saves to deny Nicky Hunt, Nicolas Anelka and Davies.
Seconds before Davies' winner, Jussi Jaaskelainen's one-handed save denied Michael Tonge on a rare Blades raid.
Blades boss Neil Warnock stripped down and re-assembled his back four, essentially picking four central defenders to cope with Bolton's aerial threat.
It looked a wise decision as Bolton typically got the ball forward quickly and got crosses in.
Gary Speed arrived to head the first from Davies narrowly wide, while Blades' keeper Kenny grabbed Kevin Nolan's cross under pressure from Nicolas Anelka.
Both keepers breathed sighs of relief as they were guilty of spillage. Jaaskelainen fluffed Colin Kazim-Richards' cross and was let-off as they ball bounced away from Christian Nade.
At the other end, Davies' shot escaped Kenny's grasp and rebounded to safety off the onrushing Nolan.
Kenny redeemed himself with two stunning saves, the first climbing to his right to tip away Hunt's volley, and then he arched to his left to claw away Anelka's curling shot.
Paddy Kenny was in inspired form for Sheffield Utd
Sheffield United were under the cosh but might have taken the lead just before the break when Keith Gillespie's shot deflected off Ricardo Gardner and clipped the outside of the post with Jaaskelainen completely wrong-footed.
Bolton won two free-kicks in promising positions at the start of the second half, with Speed driving the first one over and Anelka's effort clipping off the wall and deflecting over.
Kenny rescued his side for a third time, reacting superbly if unorthodoxly, to block Davies' close-range effort with his legs.
The Blades needed to show more ambition to stem the one-way traffic which was threatening to overwhelm them. They did that when Nick Montgomery's low shot drew a save from Jaaskelainen.
But Speed missed a great chance to put Bolton ahead when Phil Jagielka's clearance fell to him 18 yards out, but he dragged his shot wide.
The Blades were riding their luck when Davies nodded El Hadji Diouf's cross down and Anelka reacted by sticking out a leg but from three yards out he directed the ball the wrong side of the post.
Kenny belied his bulky frame and showed his speed off the mark by twice sprinting from goal to deny Anelka as he looked to latch on to through balls.
For all Kenny's heroics, it needed a brilliant one-handed save from Jaaskelainen to deny Tonge what would have an unlikely winner.
It proved to be a vital save as within seconds Davies scored Bolton's winner.
Anelka picked up a clearance and cut inside before laying the ball into Davies' path and his low, raking shot beat Kenny's dive.
Bolton boss Sam Allardyce:
"We needed the points and it was a game where the result was more important than the performance
"We made hard work of it due to a combination of poor finishing and excellent goalkeeping from Paddy Kenny.
"I was wondering if it was going to be one of those days where we were going to get punished by them on the break."
Sheffield United manager Neil Warnock
"There's no doom and gloom in our dressing room.
"I don't think we've anything to be down about, in open play we probably created more chances than they did.
"Paddy pulled off some great saves but it wasn't one sided. Their keeper had to make some great saves as well."
Bolton: Jaaskelainen, Hunt, Meite, Ben Haim, Gardner, Nolan, Faye, Speed, Davies, Anelka, Diouf (Teymourian 86).
Subs Not Used: Walker, Giannakopoulos, Thompson, Tal.
Goals: Davies 80.
Sheff Utd: Kenny, Kilgallon, Jagielka, Lucketti, Bromby, Gillespie (Shelton 82), Montgomery, Leigertwood, Tonge, Nade (Stead 64), Kazim-Richards.
Subs Not Used: Morgan, Armstrong, Geary.
Booked: Kazim-Richards, Montgomery, Kenny.
Referee: M Clattenburg (Co Durham).