Chris Wilder was visibly frustrated following United's stalemate with Cardiff City on Easter Monday.
Anthony Pilkington broke United hearts in stoppage-time after Leon Clarke's goal looked to have secured three valuable and deserved points for the Blades.
The Gaffer remarked: "We didn't get what we deserved, we played well and should have won against a team looking to get out of the division.
"We've not been clinical enough in the final third, everything else is quite good, we're playing front foot football and creating chances."
Wilder added: "We opened up a side with a good defensive record time and time again, only to get caught with the sucker punch right at the death.
"Look at the reaction from everyone associated with the opposition at the end, I understand it meant a lot, we enjoyed plenty of late goals in a promotion winning side last season.
"It's just difficult to accept that we've played so well against a side like Cardiff and for us to leave the pitch without the win the performance deserved."