Nigel Clough was bitterly disappointed to see 'big decisions' go against the Blades in the 2-1 Boxing Day defeat at Port Vale.
Ben Williamson put the home side ahead early on, before Chris Basham harshly saw a straight red from referee Stuart Attwell following a tackle on former United midfielder Michael Brown.
Jamal Campbell-Ryce levelled in the opening exchanges of the second-half, only for Dany N'Guessan to win it for Vale from the penalty spot after Bob Harris was adjudged to have fouled Mark Marshall in the box.
Speaking in the aftermath of the loss, Clough commented: "I thought we deserved something from the game. One or two big decisions went against us and the sending off which changes the course of the game wasn't a sending off in our opinion.
"We had two or three chances in the first-half though and we simply have to score from one of those opportunities, because if you don't you get punished at the other end.
"Nobody thought it was a sending off, Rob Page said as much on the touchline as did one of their defenders, but I thought the lad was seriously hurt at first when I saw him rolling around on the floor.
"But then he gets up and plays a full game. We had a few heavy challenges go in on us, but we got up and carry on.
"The tackle on Chris (O'Grady) was much worse and more dangerous in our opinion because their lad was off the ground with his studs showing, but that was only deemed to be a yellow card."
The Blades boss, who praised Jamie Murphy's contribution to United's equaliser, had no complaints over the award of the penalty though.
He added: "It was a penalty without a doubt and a silly challenge from Bob (Harris), we made some poor decisions indiviudally on the day but still derserved something from the game.
"We worked so hard with 10 men to get back on level terms, so to throw it away like we did is even more frustrating.
"It was a brilliant goal we scored though and for 20 minutes or so at the beginning of the second-half it looked like we had the extra man."
On the impending loss of Chris Basham to a three-game suspension following his dismissal, Clough concluded: "Losing Chris is a massive blow, especially with Paddy (McCarthy) scheduled to go back after Sunday, we will speak to Crystal Palace, but Neil (Warnock) has always said he wants him back for the third round of the FA Cup.
"We have got Harrison (McGahey) and Terry (Kennedy) so they will get an opportunity."