It is the physicality of standing toe-to-toe with Novak Djokovic that ultimately takes the heaviest toll.
Taylor Fritz conceded as much despite having managed to hang with the world No.1 for more than two-and-a-half hours in blazing afternoon sun on Tuesday, and after splitting the opening two sets.
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It still would have required a momentous effort to conquer that summit from there on, on a court the 36-year-old has not fallen on in a quarterfinal since 2014 when Stan Wawrinka had his number.
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Djokovic eventually improved to a flawless 9-0 against the Californian after three hours and 45 minutes. It was only the second time Fritz had managed to take a set, but both times he had done so were at this arena.
“It was two sets, but, I mean, I've played four sets in that time,” Fritz said of the 7-6(3) 4-6 6-2 6-3 result.
“It was two-and-a-half hours of really physical, like, really physical tennis.
“Yeah, it's tough to just sustain that level for, you know, probably two, three more hours that I needed to when I haven't really gotten to play at that level and play against that level that often.
“You know, it's tough to prepare for something like that … I've done what I can, but it's tough to prepare you for playing that physicality for potentially four, five hours.”
After a gruelling 15 hours and nine minutes on court already at AO 2024, Djokovic was through to an 11th semifinal at Melbourne Park.
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It is the most time he has required on court to emerge through the first five rounds of an Australian Open campaign.
“I think we both felt the effect of the heat,” Djokovic said. “You know, when you're playing on a hard court, the heat is absorbed in the surface. So down there for us players, we feel probably even more heat than you would feel in the stands. And, of course, running.
“Yeah, it's hard to put down your heart rate, you know, and kind of control your breathing. It's very intense.
“The high level of tennis and intensity exerts a lot of effort, and you feel, you know, you're spending a lot of energy and you don't have much time to recover.”
During the match, one Djokovic fan held aloft a hand-written sign cheekily teasing their idol, which read: “Have you printed your 25th Slam jersey?”
As the Serbian’s latest victim, Fritz would not be surprised to see the top seed reign again on the final Sunday.
“I think one of the biggest things is, like, just the fact that … he's so fast he doesn't really miss a lot of balls,” the 12th seed said.
“He definitely makes you really work and, like, hit quality shots to win points. It's also just like the lack of free points he gives you.
“That's also why we're playing so the first two sets are so long, as well. It's, like, I never just hit a second serve and he just misses it. That just doesn't happen. Even when I'm going after my second serve, like hitting second serves that are consistently like 100, 105 miles per hour, like jamming him, he still just puts it on the baseline.
“It's definitely tough when you don't get those free points and you have to work for every single point.”
A decade younger, Fritz scoffed at the suggestion his conqueror was showing any signs of losing his edge.
“No,” he grinned.
“From what I can recall from the first times we've played, to me, I think he's just as good as ever.”