Boss Nigel Clough admitted the Blades only had themselves to blame for Saturday's 2-1 home defeat to Gillingham.
Two defensive lapses at the start of each half paved the way for a victory for Peter Taylor's men, as Clough tasted defeat for the first time as United boss at Bramall Lane.
Speaking in the aftermath of the reversal, he commented: "It was a game that was there for the taking, but to give two goals away in the manner we did makes it very difficult to win any match.
"Sometimes you label goals as schoolboy defending, but the first goal is worse than that. Harry (Maguire) has been immaculate since the day we arrived, but he made a massive mistake and the opening goal gave Gillingham a massive lift.
"When Gillingham got their noses back in front, we knew it would be very tough to break them down again and so it proved, but the biggest disappointment is to concede at the beginning of each half.
"George (Long) has hardly had a save to make again, yet we have conceded another two goals. It is hugely frustrating, because we should have won the game."
Clough pinpointed the turning point of the League One clash, adding: "Their second goal flattened us and gave them an unbelievable boost, we came out at the start of the second-half firmly believing the game was there to be won, but unfortunately it didn't work out that way and that is hard to accept.
"Because we were chasing the game we went long too quickly, ultimately we wanted to get the ball into the penalty area, but we wanted to do that from good positions and we perhaps became a little nervous and too eager to get back into the game."