Andy Murray felt he came up short in a stamina test after Novak Djokovic knocked him out of the US Open at the quarter-final stage.
World number one Djokovic won 7-6 (7-1) 6-7 (1-7) 6-2 6-4 at Flushing Meadows on Wednesday to end Murray's hopes of claiming the grand slam event for a second time.
Murray made the top seed work for his place in the last four, but the British number one was left to admit that the Serb had a physical edge over him.
"I would say physically he was fresher towards the end," Murray said.
"I tried to hang in as best I could in the fourth set. He was definitely, well he appeared fresher than me. Whether he was or not I don't know.
"Maybe he does a better job at hiding it than me. The pace of my serve slowed significantly towards the end of the third set.
"In matches when you play against him or anyone at that level there is going to be periods in the match when they are going to play better, your level is going to drop a little bit.
"It happened to him a couple of time in the first set and in the second set as well. Just over the course of the match he was a little more solid than me. Definitely fresher at the end so that helped.
"I played well, especially the first couple of sets there was some good tennis. I played a poor tie-break in the first set definitely and a good tie-break [in the second].
"I was down in the first set and I fought back I was down in the second set and a break and fought back. I played some good tennis but it wasn't enough.
"I'm obviously disappointed, it's extremely late, I am tired and don't feel particularly proud right now, I feel disappointed. I think there was some good tennis.
"I haven't analysed the match or had time to think about it yet but I think there was some good tennis there. Hopefully I can build on that."