Carlos Alcaraz was determined fatigue would not get the better of his US Open title tilt, but he accepted he was "a little bit" tired after defeating Casper Ruud in Sunday's final.
Alcaraz set a grand slam record for the most time spent on court at a single tournament, in large part due to playing five-set matches in the fourth round, quarter-finals and semi-finals.
Still, the 19-year-old had enough energy left to take down Ruud in four sets, with his 6-4 2-6 7-6 (7-1) 6-3 victory making him a first-time major champion and the new world number one.
Asked if he would now acknowledge the effects of this run on him, Alcaraz replied: "A little bit.
"I always say it's not time to be tired in the final round of a grand slam or any tournament; you have to give everything on court, everything you have inside. It's something I work really, really hard on."
Alcaraz is the youngest player to ever sit atop the men's rankings, and he added: "This is something I dreamt of since I was a kid, to be number one in the world, to be a champion of a grand slam.
"It's something I worked really, really hard for. It's tough to talk right now. There's a lot of emotions right now.
"This is something I tried to achieve. All the hard work I did with my team, my family... I'm just 19 years old, so all the tough decisions are with my parents, my team as well. This is something that is really, really special for me."