The West Londoners twice lead through goals from Thiago Silva and Noni Madueke, but there could be few complaints as their bottom-placed hosts earned a deserved point, regardless of the circumstances.
Jayden Bogle got the Blades back on level terms in the first half, before Oli McBurnie reacted fastest to a flick-on in the third minute of added-on time to fire past Djordje Petrovic from close range.
However, it is a result that suits neither side, Chelsea sitting in ninth and five points behind sixth-placed Manchester United, with Sheffield United nine points adrift of safety in the table.
Mauricio Pochettino made the decision to make three changes for a game being played just three days after the dramatic 4-3 victory over Manchester United on Thursday, and it was one of those players who made an immediate impact.
An outswinging corner from Conor Gallagher found Silva unmarked by the penalty spot, and the veteran defender found the far bottom corner of the net with a volley.
Although Silva made a positive contribution at one end, he almost undid that at the other, a weak pass to goalkeeper Djordje Petrovic being seized upon by McBurnie, who pulled the ball back for Ben Brereton Diaz only for Moises Caicedo to make a timely block.
While Chelsea were still showing a threat going forward, Sheffield United were becoming the better side, and soon after Petrovic had done well to keep out a Gustavo Hamer effort, the midfielder turned provider for his side's equaliser.
The former Coventry City man picked out the run of Bogle with a through-ball and rather than pull the ball back from a tight angle, the wing-back deceived Petrovic at the near post with the goalkeeper only diverting a shot into the roof of the net.
Sheffield United picked up where they had left off at the beginning of the second half, McBurnie heading wide from a Brereton Diaz cross as the pair continued to get the better of the Chelsea backline.
Hamer also tried to get in on the act, a rasping drive fizzing just wide of the post with Petrovic beaten, and the home side were ultimately made to pay as Madueke put Chelsea back in front.
After receiving a pass on the right flank, the England Under-21 international cut inside before drilling a shot into the bottom corner from 16 yards out.
Cole Palmer soon forced Ivo Grbic into tipping his 25-yard strike over the crossbar before he was withdrawn, a time when Sheffield United were ready to mount their bid for a leveller.
Heading into five minutes of added-on time, it felt like Chelsea would hold on, but McBurnie had other ideas, the Scot latching onto a loose ball inside the penalty area to fire into the bottom corner, Petrovic left with no chance.