NEW YORK -- Stan Wawrinka has undergone the most comprehensive 18-month transformation of any tennis professional in recent memory, to the point where he now stands a good chance of ruining a big day for Roger Federer, the longtime friend and countryman in whose shadow he once comfortably languished.
The two will meet in the semifinals of the US Open on Friday, a pair of over-30 Swiss men who have brought a double dose of glory to their tiny nation. Federer's role in that glory is a well-known saga of steady, unparalleled excellence; Wawrinka's is the more unlikely, but suddenly rich narrative.
For a long time, Wawrinka was known as a talented, brawny but inconsistent player, a perpetual work in progress. He was a top contender (along with Federer) in the popular "best one-handed backhand" derby, but unlike that of his fellow countryman, that backhand didn't carve out the big titles.
Federer was a friend, and certainly a role mode. But he was also a rebuke and an implicit challenge: keep up, get better. Wawrinka didn't always enjoy the pressure; it was easier to plow along as that guy with a lot potential but so-so results, Federer's wingman.
Wawrinka always said the right things about Federer, and the reigning French Open champ did the right things, which consisted primarily of playing doubles alongside Federer when needed (they won Olympic gold in Beijing) and losing to Federer in singles.
Federer led their head-to-head 2-0 when Wawrinka first beat him in Monte Carlo in 2009. Federer then reeled off 10 straight wins before Wawrinka swept him aside in his title run at the same event in 2014, by which time Wawrinka was a profoundly different player, despite still trailing in the rivalry, 13-2.
"I think a lot [of success] came through practice for Stan," Federer said on Thursday, after he swept aside Richard Gasquet in the quarterfinals. "It took him a while to figure out exactly what the possibilities were; I don't think he was a guy who always had enough confidence. Something was holding him back, maybe."
Between figuring out where he fit in the Swiss picture, learning how to compete with Federer without alienating him, finding self-belief and ironing out the kinks in his serve, forehand and fitness, Wawrinka had his plate full. But he figured it out at age 29, when he won the Australian Open and -- fittingly -- Monte Carlo.
Wawrinka shot up to No. 4 in the world but experienced a few glitches backing up his newfound status at the majors. Then, earlier this year, he stunned top-seeded and heavily favored Novak Djokovic in the French Open final. More to the point, Wawrinka crushed Federer in the quarterfinals without losing a set.
"I think now we're both nervous when we enter the court now," Wawrinka said of the new dynamic in his relationship with Federer after the quarterfinals. "Before, it was only me. I was nervous because I knew I wasn't at his level, for sure."
But thus far, Wawrinka has demonstrated that he's at Federer's level only on red clay. All three of Wawrinka's wins have come on the surface. It isn't because he's more consistent than Federer, which would be the tempting assumption to make. It's because the clay gives Wawrinka, who's still a ponderous mover despite the gains he's made in fitness, a little extra time to set up and draw a bead when the ball is coming his way.
Wawrinka won't have that luxury on the medium-fast hard court on Arthur Ashe stadium, especially not if Federer continues to play with the derring-do of recent days, the full-on offense that's become the talk of all tennis. His dazzling speed, mobility and racket work have been amazing.
"I'm looking a lot at what the top guys are doing," Wawrinka admitted in a refreshingly humble moment. "I always try to see why [Djokovic, Federer and Rafael Nadal] are so good."
After watching Federer play Kevin Anderson in Cincinnati, Wawrinka noticed how Federer dared to move inside the baseline to take the serve -- a seemingly suicidal tactic against a power server like Anderson. But it worked, because it took time away from Anderson if Federer made the return.
Wawrinka incorporated the tactic into his game plan, and it helped account for the discomfort Anderson felt in a straight-sets loss Wednesday at the US Open.
Look for Wawrinka to play aggressively, inside the court, doing everything in his power to push Federer back.
"It's going to be tough because [Federer] is serving really well since the beginning of the tournament," Wawrinka said. "I'm not going to have many opportunities. I will have to play really, really fast, be the aggressive player if I want to have a chance to beat him."
Given their careers, biographical details and personal relationship, you can't help but wonder if Federer and Wawrinka don't feel almost like siblings, with Federer playing the role of older brother. A reporter the other day wondered if that might be problematic for the all-time men's Grand Slam champion.
"It's not so hard for me, I have always found it quite -- not easy, but it's just another match," Federer said. "I'm able to see it somehow that way with Stan."
Of course, there's another dimension to their closeness, which is the intimate knowledge they possess of each other's most closely guarded tennis secrets.
"Of course, subconsciously you know that he knows what your preferences are," Federer said. "Where you like to go, where you're probably going to go. Probably he feels the same way. That's the weird part. I feel we meet each other somewhere in our minds before the point is being played out."
That mind game probably won't go as far as the umpire's chair levitating or either man bending the other's racket with his mind. And you can be sure neither of them will want to bend his racket over the other's head.
"You know, I'm the first fan [of Roger] for many years," Wawrinka said. "Always watch his big matches. Always happy for him, with all the titles he's got. We are good friends. Really close friends. Always laugh together. Friday [in the semis], we gonna laugh together in the locker room because we have lockers next to each other. We each gonna try to win, then after the match, it's back to normal."
Back to the new normal, he might have said, in which the question is: Who's going to have the last laugh?