Nigel Clough felt his side were unfortunate losers, following the 2-0 reversal against Shrewsbury Town on Saturday.
With the Blades trailing 1-0 at the break, Clough introduced Febian Brandy owing to a facial injury to Neill Collins, but the dismissal of the former Walsall forward just before the hour for violent conduct proved to be the decisive moment of the clash at the New Meadow.
Speaking afterwards, the Gaffer remarked: "I am bitterly dissapointed with the result, but we can take plenty of positives, which is a bit strange when you have lost 2-0.
"We conceded to a fantastic strike just before half-time, then ill discipline in the second-half costs us the chance of getting a point, if not all three.
"The attitude, application and effort was excellent though, particularly with ten men, we kept plugging away and still created chances.
"We felt we were in control of the game for long periods and until the sending off we were starting to crank up the pressure in the second-half kicking towards our supporters.
"Aidy (White) supplied a terrific ball in from the left and on other day one of our strikers adds a finishing touch.
"Overall though we didn't make the Shrewsbury goalkeeper work enough. We got a lot of balls into the box and had several shots over the top, but we really should have made him work more."