Nigel Clough, backed up by conclusive replays post-match, felt key decisions went against the Blades at the Proact Stadium on Saturday.
In the Sky Bet League One derby clash, Chesterfield eventually ran out 3-2 winners in a game that also saw a player from each side given a straight red card in the first half, Michael Higdon for the Blades and Spireites goalkeeper Tommy Lee.
But, as members of the media witnessed in the aftermath of the contest, three offside decisions appeared unjust on the visitors and despite Marc McNulty and Neill Collins netting in the last ten minutes, United returned home from Derbyshire with nothing to show for their efforts.
Summing up his feelings, Clough, who admitted Higdon's tackle gave referee Mark Brown the chance to brandish the red card, remarked:
"Decisions changed the game from the first minute to the last, although we didn't help ourselves at times.
"Michael's tackle was, in our opinion, a yellow card, but Jamie Murphy was brought down when clean through in the 17th minute and nothing was given, that was the turning point of the game.
"Michael didn't need to make the tackle and it is disappointing when experienced players make bad decisions, the same goes for Paddy McCarthy for the second goal, he knows he should have just cleared his lines.
"If we could have gone in at 1-0, with 10 v 10 with 45 minutes to go, then we could have regrouped and gone on to get something from the game."
The Gaffer added: "Their first goal was a screamer, the second in as many matches, until then it was a typical derby, with little in the game.
"Chasing the game in the second-half we were always vulnerable on the break and that is Chesterfield's strength, but replays suggest the third goal is offside and replays also show a few other offside decisions appeared harsh on us.
"We have to move on, though, and keep trying to find ways to stop leaking goals away from home."