Nigel Clough hailed the Blades following a tenth consecutive victory in all competitions against Carlisle United on Wednesday.
Jose Baxter's excellent first-half strike settled the contest, despite the Cumbrians mounting a spirited second-half effort and Clough was understandably delighted as United made it a perfect ten.
Speaking afterwards, the manager remarked: "We are incredibly proud of what the players have achieved. Ten straight wins in all competitions is something, but to have kept nine clean sheets in the process in quite staggering.
"As the second-half progress we were dead on our feet but sheer determination, desire and character got us over the line.
"Carlisle gave us a real test, especially in the last 30 minutes or so. The crowd were urging us on and we were trying to get forward, but fatigue had kicked in and we struggled to influence the game as we would have liked.
"But if you can't get that second goal which makes the game safe, you have to look after the one you already have and we dug in, it was backs to the wall but again we defended admirably.
"Mark (Howard) wasn't overworked, but he was decisive when he came to take crosses or make punches. The protection he received in front of him was once again tremendous and we can't praise the players enough."