Vincent Kompany claims Burnley hit a wall in defeat against Sheffield United at Bramall Lane
The Clarets boss conceded that the visitors hit a wall in the second half as Paul Heckingbotham's side scored four times to close the gap at the top of the Championship.
Burnley led through Manuel Benson's double at the interval, with Iliman Ndiaye equalising in-between, but there was a significant shift of moment after the break and the Blades capitalised.
"The first half, when we had the ball, we were dangerous, and it looked like we had momentum going forward," said Kompany. "In the second half I think I've asked as much as I can of the players, I think we just physically collapsed after coming to the end of a difficult period.
"The lads have done ever so well to always be on the front foot, to be aggressive and always going after teams, but we ended up going on the back foot in the second half.
"There wasn't anything we could get out of the team. After conceding the goal so early in the second half the momentum just shifted and it was a tough second half."
Four of the home side's five goals came from crosses into the box, either from open play or set-pieces, as the league leaders struggled to compete with second phases of play.
Ndiaye guided the ball home from Oli McBurnie's header from a corner before the Scottish striker threw himself at Anel Ahmedhodzic's header from a Jack Robinson delivery to level for a second time in the 48th minute.
The latter then flicked an effort past Arijanet Muric from close range after Ahmedhodzic's header had come back off the bar from another corner, but the Bosnian defender managed to get himself on the scoresheet when Oliver Norwood's set-piece was steered back into the box.
McBurnie later rounded things off when tucking the ball into an empty net after George Baldock had drawn the save from Muric following Norwood's pass over the top.
However, Kompany feels those moments don't happen if his side's energy levels hadn't waned. "A big part of our game is that we're on the front foot, so before you get a cross in you've got to get over the halfway line, when you put in a long ball over the halfway line, you've got to win the second balls and we're extremely aggressive on that," he said.
"We've always got numbers in the middle of the pitch, and when we have the ball we look after it, which makes it difficult [for the opposition] to get into the areas where you have crosses and set-pieces. A big part of our game disappeared in the second half because we just couldn't go after them any more.
"I've got to be understanding. I could see it in their eyes; it wasn't for a lack of wanting, they just weren't able to. It doesn't surprise me that the first half was good and the second half was when we had the collapse. It just makes sense."