United, who were in the relegation zone as recently as mid-February, have surged up the table in a run of form that has also seen them reach the semi-finals of the FA Cup.
But they were perhaps lucky to get a point from their trip to the fourth-placed Preston, who controlled proceedings in the second half.
Josh Brownhill was denied by the post in the 55th minute for Preston, with his right-footed effort crashing into the woodwork after Paul Gallagher set him up.
Gallagher then had a goal disallowed in the 74th minute for being offside, after shooting past Sheffield United goalkeeper Mark Howard.
Preston continued to dominate but even the late introduction of Kevin Davies failed to help, as they were made to rue a night of missed chances.
The draw has extended Preston's unbeaten run to nine matches in all competitions, while Sheffield United remain 10th.
