Alan Knill felt the Blades had enough of Sunday's Emirates FA Cup tie against Bolton Wanderers to get a positive result, but admitted the home side were better at both ends of the pitch.
Despite second-half goals from Paul Coutts and Jack O'Connell, United were undone 3-2 in Lancashire, as the Trotters advanced to Monday's third round draw.
Reflecting on the loss at the Macron Stadium, Chris Wilder's number two remarked: "It's very disappointing, especially when you've had enough of the game to get a result, but unfortunately it is what happens in both boxes that really counts.
"They were ruthless, we created chances to score more goals and didn't take them, that's ultimately why we've lost the game.
"We don't want to be the best team but lose the game, it was very similar to Tuesday against Walsall, when we should have won comfortably."
Knill added: "We were very good in the middle of the park, we moved the ball round excellently at times, but it is about keeping it out of your goal and putting it in theirs and we haven't been good enough at that.
"We are disappointed with the goals we conceded. The first one is a set-piece and we knew how strong the opposition are from them, the second one straight after half-time gives us a mountain to climb and the third one is too easy.
"We did show some fight, but you can't create the number of chances we are creating and not make them count."