Matt Done had put the Blades in front, but the hosts were level inside two minutes via Ash Hunter.
And it got worse for Nigel Adkins’s side when Marcus Nilsson fired Fleetwood in front on the hour.
The hosts were down to 10 men when Nick Haughton was shown a second yellow card, and Che Adams converted a stoppage-time penalty to earn United a point.
The draw leaves United six points off the play-offs, and sixth-placed Barnsley.
Blades boss Adkins was unhappy to see John Brayford’s effort ruled out.
“We’ve dominated the game, haven’t we?” said Adkins. “We’ve responded really well, created plenty of chances. We should have had a penalty in the first half, it was plain to see.
“Saying that the two goals we conceded were shocking, just simple balls from out wide.
“But we’ve played some good football and have had two cleared off the line.
“John Brayford’s goal at the end is a clear goal and the referee gives a free-kick and it’s not. It’s a goal, there’s no foul at all.
“It’s annoying because we’ve played some good football, created lots of chances and only come away with a point.
“The players have responded really well. I’m just annoyed we haven’t got the three points we deserved.”
Fleetwood boss Steven Pressley felt a controversial penalty, after Ryan Flynn was fouled in the box, cost his side all three points
“I felt we had just done enough to win the game and in the end a controversial penalty has cost us the game which is disappointing,” he said.
“I was too emotional after the game and haven’t got round to watching the incident again. The players believe that it wasn’t a penalty.”
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