Novak Djokovic gave credit to Andy Murray after beating the British number one to reach the semi-finals of the US Open.
Top seed Djokovic prevailed 7-6 (7-1) 6-7 (1-7) 6-2 6-4 in a hard-fought quarter-final at Flushing Meadows on Wednesday to stay on course for his eighth grand slam title.
Murray, the eighth seed, was made to pay for 18 unforced errors in the fourth set as he crashed out of the tournament.
Djokovic will face Japanese 10th seed Kei Nishikori in the last four and the world number one was relieved to come through another test of his stamina after admitting he was not at his best against Murray.
"I'm happy that I managed to pull through physically at the end and stay strong even though it was frustrating in moments, because I don't think I played at the level that I wanted to play on in important moments." he said.
"But again it's credit to Andy because we always push each other to the limits and put a lot of pressure on each other's service games.
"Quarter-finals of a grand slam, playing each other in a close match, you're not going to win it by staying back. You're going to win it by pressuring your opponent, hitting angles and coming into the net.
"That's what he tried to do. Obviously he struggled a little bit with his lower back in the fourth and he didn't serve as accurately as he did in the first part of the match so that gave me more possibilities to step in."