Andy Murray felt fitness played a crucial role during Sunday's fourth-round win over Grigor Dimitrov at the Australian Open.
Murray " a three-time finalist at Melbourne Park " won through to the quarter-finals via a 6-4 6-7 (5-7) 6-3 7-5 triumph after three hours and 32 minutes on Rod Laver Arena.
Dimitrov made a bright start to the match before eventually losing the opening set.
The Bulgarian 10th seed - leading 5-2 in the fourth - then had the chance to force a fifth and deciding set but he faltered dramatically as Murray won five unanswered games to progress.
Speaking to reporters afterwards, Murray said he had picked up on Dimitrov's fading energy levels and took full advantage by extending the rallies.
"I felt like he, in the fourth set, was trying to shorten a lot of the points," said the 27-year-old Brit, who will face Australian teenager Nick Kyrgios in the next round.
"If you went back and watched it, especially when he got ahead, he was trying to come forward a lot.
"Then, on my service games, he was going for broke a little bit off my serves. First and second serves he was going for big returns.
"So I felt like maybe he was tired. I don't know if he was, but that was the feeling I got with the way he was playing at that stage.
"I tried to, towards the end of the set, extend the rallies. And physically I felt completely different to how I felt at the US Open last year or even here last year when I played a long match, especially in cold conditions."
Murray was slow to find his rhythm but he was a force to be reckoned with once he did.
The two-time grand slam champion posted 42 winners over the four sets, while he limited his unforced errors to just 35, compared to Dimitrov's 51.
"I thought I played well. I thought he started the match extremely well," Murray added.
"He came out very aggressive, very explosive. But, you know, it's tough to keep that sort of level of intensity up. And then, yeah, once I got myself into the match, I felt like I was able to dictate a lot of the points.
"I thought tactically I played a good match. I was disappointed with the 6-5 game I played in the second set. Also the tie-break, I made a few bad decisions.
"Third set was good. And fourth set, I just fought hard at the end and he played a loose game when he served for the set. That was it."