-- NEW YORK -- Well into the fourth set, he sat slumped in his changeover chair, a towel draped over his head, apparently lost in some sort of Zen trance.
In fairness, the past two months of Novak Djokovic's 2016 season have been tumultuous, to say the least.
After completing his career Grand Slam at Roland Garros, the No. 1-ranked Serb was bounced in the third round of Wimbledon, saw his "private issues" set off a tabloid feeding frenzy and lost in the first round at the Rio Olympics. Upon his arrival in New York, he acknowledged a recurring left wrist injury.
But amid the chaos, Djokovic still has an opportunity to make a special kind of history: With a title here at the US Open, he and Roger Federer would be the only men to win three Grand Slam singles championships in a single season -- three different times. Djokovic and Rod Laver are the only ones besides Federer to do it twice.
So, one of the leading questions of the fortnight: Can Djokovic check all that baggage at the door and focus on the daunting task at hand? Will he even be in the building when the finals and, presumably, the momentum-aplenty Andy Murray roll around?
The early returns, as it were, were inconclusive. In the first US Open night match under Arthur Ashe Stadium's new roof on Monday night, Djokovic never looked completely comfortable in taking out Jerzy Janowicz 6-3, 5-7, 6-2, 6-1.
There was, of course, drama -- how could there not be? Djokovic called for the ATP World Tour trainer in the first set to work on his right arm and, on a few occasions, grabbed at that offending limb. And then, Janowicz ran off with the second set. But Djokovic, scuffling, scrambling, sneakers squeaking under duress, bore down and produced a thoroughly professional win. There was even a sneaky serve-and-volley that helped nail down the third set.
When it was over -- 2 hours and 37 minutes after it began -- Djokovic looked weary and quite relieved. The first on-court question concerned his health.
"Thank you for staying this late," Djokovic told the crowd. "It was hard to put up a show after Phil Collins."
And then he broke into a song, "I Can't Dance," made popular by the drummer's former band, Genesis. Collins performed on opening night at Arthur Ashe Stadium.
"I can't dance, I can't talk," Djokovic sang. "The only thing about me is the way I walk.
"Sorry, sorry. I had to do it. I promised myself I'm going to do it."
Djokovic did not address his wrist and arm injuries until prodded a second time.
"Look you know, it's never easy to play at this level throughout the year," he said eventually. "There are days and weeks when you're not feeling you're 100 percent.
"I don't think it's necessary to talk about this now."
There will be plenty of time for that before Wednesday's second-round match against Jiri Vesely, who beat Djokovic in their only meeting, earlier this year in Monte Carlo.
Ultimately, this was a predictable first-time result -- an outcome actors Alec Baldwin and Susan Sarandon, fashion designer Vera Wang, former boxer Mike Tyson and chef Emeril Lagasse probably came out to see -- between players who are ranked No. 1 and No. 247 in the world.
Djokovic has never, ever lost a Grand Slam match to a player ranked outside the top 100; he pushed his record to 33-0. The winner of the season's first two Slams, the Australian Open and French Open, Djokovic is a scalding 52-5 for the year.
Janowicz, on the other hand, has yet to win an ATP-level match this year. A surprise Wimbledon semifinalist three years ago, the 25-year-old Pole was forced to sit out between January and July with knee and back injuries.
The 2007 junior finalist has lost his past five Grand Slam singles matches and is still looking for his second career US Open win. But there were real flashes that suggest he'll soon be competitive again.
When it was over, Djokovic slowly walked toward the net with an exceptionally somber expression on his face. Even his signature celebration to all four corners of the arena seemed to take unusual concentration and effort.
Djokovic finds himself the defending US Open champion and seeks his third title overall. He's now a sparkling 20-1 in Arthur Ashe night matches at the US Open.
"I feel like when I step in here, it's in a dark tunnel but there is always a light," Djokovic said. "At Arthur Ashe, there is always a light at the end of the tunnel."
Right now, that light looks awfully far away.