After Matt Phillips’ strike was cancelled out by Jayden Bogle, Ramsdale made a point-blank save to deny Callum Robinson putting his side back into the lead.
Billy Sharp went on to win the game for the Blades and Allardyce was left rueing that save.
“It came down to two moments with balls in our box that we didn’t deal with correctly, two very scruffy goals that could’ve been avoided,” he said.
“A lot of what we talk about has happened again tonight after trying to make players aware of the situation. Particularly the defenders. I’m dealing with the situation as it arises.
“They were just about to bring Billy Sharp off and all of a sudden his last moment in the game ends up with him scoring the goal. What would have happened if it was a few seconds later.
“But the biggest moment in this game, apart from me being very disappointed at the two goals we conceded, was the save from Ramsdale on Callum Robinson.
“That would have been us 2-1 up at that stage of the game.
“I have to say that with our defensive frailties we might not have won the game from there, but we wouldn’t have lost it. It would have been another point, it might’ve been all three.
“That moment came and went and it was the biggest defining moment in the game for me.”
After making two loan signings on transfer deadline day, Allardyce is hoping they can help his side ‘turn a corner’ in the coming weeks.
When asked how damaging the defeat was, he added: “It’s very damaging because we play a game of football not to lose and we keep losing far too many.
“I’ve done my best to help the squad. The club has done the best to help the squad that’s already here. We’ve done all we can possibly do in terms of improving the squad.
“We hope that the players who have come along to join the fight can make a big contribution as quickly as possible.
“That might not be as easy for Okay (Yokuslu) from Spain and obviously with Mbaye (Diagne) catching up with the pace of the Premier League.
“Certainly with Robert Snodgrass’ experience and Ainsley (Maitland-Niles), an England international, will hopefully lift the players and show the quality we know they’ve got.
“We have to turn the corner and start picking up points. When we start picking up points per game, which we should’ve done over the last two games.
“We should have seen the game out at Fulham being in the lead and we shouldn’t have lost today.
“Four points out of two games would have been great and now we only have one. We only have ourselves to blame.”