Speaking after Tuesday's FA Youth Cup exit at the hands of Reading, Coach Travis Binnion was proud of his players, but left thinking about what might have been following defeat at the Madejski Stadium.
Striker Connor Hall fired the Blades in front in the 51st minute and a place in the fourth round beckoned for United until the Royals struck in the first minute of injury-time.
Then in extra-time Reading took control of the game after United goalkeeper Aaron Ramsdale was shown a red card. The home side scored the resulting penalty and added a third with the last kick of the tie.
And reflecting on the clash in Berkshire which was watched by first-team boss Nigel Adkins, Binnion admitted his youngsters should have seen the game out.
He remarked: "We should have won the game to be honest. We had worked so hard to put ourselves in the ascendancy and had defended resolutely right through until the 91st minute.
"We were three minutes away from the fourth round then we make a simple mistake, give possession away and then don't defend the corner.
"In my opinion we then looked the stronger side in extra time and the most likely to nick a goal, until Aaron (Ramsdale) is sent off and they score from the penalty.
"That was a crushing blow and from then on we never really looked like coming back, the third goal is harsh on us, but one of those things and our players should remain proud of themselves.
"It was a good effort, but ultimately not quite good enough as we come up agonisingly short."
Looking ahead, Binnion is confident of signing off 2015 in style on Saturday, adding: "Now we have to learn from the experience, starting against Hull at the weekend.
"Good sides react positively and bounce back, that's what we want to see from the players in the coming weeks."