Moving so swiftly and smoothly that his sneakers did not betray him with squeaks, Federer was only a few feet from the service box when the ball landed. He stretched for a deft backhand half-volley, which induced the scrambling Darcis to send back a short blooper. Federer, rising, torched it with an overhead and the pleased patrons sitting in Arthur Ashe Stadium fairly buzzed.
The serve-and-volley play was once a standard for fast surfaces, a sneak attack designed to unsettle opponents and rush them into mistakes. Introducing Federer's newly minted retro defensive version -- the serve and half-volley.
"It is nice to see a guy at net and a guy trying to pass a good net player," Federer said after the match, referencing Pete Sampras versus Andre Agassi and John McEnroe against Bjorn Borg. "I saw that play growing up. It's something I feel comfortable doing.
"Clearly, I'm quite happy to be able to bring it back to some extent, and that it's actually working. ... "Many of the guys think it's quite funny. It's good, you know, I guess."
To keep up with the kids, Federer -- at the late, great age of 34 -- has been forced to reinvent himself. He's got a bigger more powerful racket, and now he's got a signature trick shot that utilizes his unique attributes of vision, timing and hand-eye coordination.
It was all part of the package Thursday night, another mesmerizing performance form the 17-time Grand Slam champion. He schooled Darcis 6-1, 6-2, 6-1 on his way to the third round, where he'll play No. 29 seed Philipp Kohlschreiber.
"I hope to be able to keep it up," Federer said after his first-round match. "When you miss, it looks ridiculous. But my coach [Stefan Edberg] says keep going for it.
"Sometimes I stand there and I'm like, 'Should I or shouldn't I?' "And then it's like, 'OK, whatever, I'm going.'"
Federer unveiled the surprise shot recently in Cincinnati during wins over Kevin Anderson, Andy Murray and Novak Djokovic. It's a dashing addition to the vast catalogue he already possesses, another tool in the game's biggest toolbox.
Maybe it's just a phase the father of four is going through. Perhaps it's boredom. Or could he be challenging himself when few others can? Is he ratcheting up the degree of difficulty for his own amusement?
Looking ahead, though, it might give him a tactical advantage when he desperately needs it. At an age when he's clearly lost a bit of his quickness, this grip and charge can suddenly level the field. By shrinking the court and relying on his dazzling volleying skills, Federer is aggressively forcing the issue.
Against Darcis, all this new-found aggression was on display. In the fourth game of the third set, Federer won the first point with an overhead that saw him more than two feet off the ground at the point of impact; his hang time was vaguely Jordanesque and left the fans oohing and aahing again.
On the next point, clearly feeling it, Federer crowded Darcis' serve with another half-volley and, after another futile reply, knocked off a sharply angled backhand overhead.
Temper your enthusiasm, fans of Federer. This was only a second-round match against the No. 66-ranked player in the world. Darcis famously upset Rafael Nadal in the first round at Wimbledon two years ago, but it was more than two years before the Belgian won his next major match -- when Marcos Baghdatis retired on Tuesday.
It was over in 80 minutes, and the five-time US Open champion has now lost a total of nine games in six sets.
There was a milestone, too. Federer has now won more night matches at the US Open than any men's player, surpassing Andre Agassi's total of 28. He's now tied, appropriately, at 29 with Serena Williams.
"I didn't know about it," Federer said, "so it's very cool. Of course I've enjoyed myself, so many times so many years. It's wonderful I can experience it.
"I hope this is not my last one, of course."
Federer hasn't dropped a service game since turning 34. Going back to Cincinnati, where he won his seventh title, he's held 72 straight times, winning 16 straight sets.
On this trip to New York, Federer recently visited the Metropolitan Museum of Art with his six-year-old twins, Charlene Riva and Myla Rose. He wanted them to see the China exhibit. Understandably, Federer drew his share of stares.
"People go there to see art, not me," Federer said in his on-court interview. "That's what I tell them. Look at the, art not me."
He's wrong, of course.
Take a picture of that half-volley, frame it and hang it alongside the Rembrandts, Goyas and Monets. Roger Federer isn't merely an artist, he is art.