MELBOURNE, Australia -- If he wasn't convinced before Tuesday, Jack Sock knew for sure after his four-set first-round victory in the oppressive heat that engulfed Melbourne Park, that he was doing something right.
It wasn't always like that, however, for the 21-year-old Nebraska native and 95th-ranked player, who defeated 78th-ranked Tobias Kamke 7-6 (5), 5-7, 6-2, 6-4 -- one of just three American men to advance to the second round of the Australian Open.
The only seeded American man, John Isner, retired with a recurring ankle injury against Martin Klizan while the other American men in action Tuesday – Bradley Klahn (to 22nd seed Grigor Dimitrov), Rhyne Williams (to Juan Martin del Potro) and Ryan Harrison (to Gael Monfils) -- were all eliminated.
For Sock, there was no greater sign of his improved fitness than conditions that Tuesday reached a high of 108 degrees.
"There were guys playing at the same time I heard had cramped or were feeling it, and I felt great at the end of the match and throughout the fourth set, and if it needed to go five, I was ready," he said.
It is, Sock admits, a dramatic change from his fitness level when he turned pro in 2011.
"I think I probably just didn't accept it," he said. "I think I knew what I had to do but I was just trying to get by and kind of just go off either talent or skills or whatever."
Sock said his agent, family and friends all had conversations with him about raising his workouts a notch or two.
"I think I probably always knew it in the back of my head," he said. "You just see those top guys playing six-hour matches and they look like they're warming up. It's outrageous but that's what it takes in today's game to be successful and able to make a living at this and achieve the things everyone wants to achieve. I think the last couple months, I just looked at myself in the mirror and figured out what I need to do and now I'm ready to go and have a great mindset going."
He will certainly need it in his second-round match against one of the more exciting players on tour, the 25th-seeded Monfils.
"He's one of a kind, that's for sure," Sock said of Monfils. "He's very exciting to watch, is spunky, has his own style and covers the court better than anyone probably."