So, Denis Shapovalov, do tell: It can't really be the case that 18-year-olds like yourself never get tired, right?
"No, it's true. We don't," the Canadian joked Friday after becoming the youngest man to reach the U.S. Open's fourth round since Michael Chang in 1989.
Shapovalov needed to go through three qualifying matches just to get into the main draw at Flushing Meadows, so he has played half-dozen time in an 11-day span.
"It's been a long ride," said Shapovalov, who was born in Israel to Russian parents and moved when he was a baby to Canada. "It feels like I have been here a month already."
There will be a first-time Grand Slam finalist at the U.S. Open now that 2014 champion Marin Cilic exited in the third round — and the entertaining-on-court, engaging-off-it Shapovalov is one of those who still have a shot at getting that far.
Just 2 1/2 months after his runner-up finish at Wimbledon, the No. 5-seeded Cilic bowed out with 80 unforced errors in a 4-6, 7-5, 7-5, 6-4 loss to No. 29 Diego Schwartzman of Argentina.
Not much later, Shapovalov advanced when Kyle Edmund of Britain stopped playing in the fourth set because of an injured neck.
"It's never great to win this way," Shapovalov said. "Hopefully, it's nothing too serious."
Neither he nor Schwartzman had ever been to a major's fourth round before, nor had another of the afternoon's winners, 35-year-old Paolo Lorenzi of Italy, who actually began his Grand Slam career with a 0-13 record.
As it is, Cilic was the only owner of a major title on the entire bottom half of the draw when the tournament began.
"That's right: A few surprises and lots of withdrawals," Schwartzman noted. "This is the moment to take advantage."
That part of the bracket originally included three-time Grand Slam champion Andy Murray, but he withdrew because of a hip injury, part of a depleted-at-the-outset field also missing Novak Djokovic, Stan Wawrinka, Kei Nishikori and Milos Raonic.
"It's kind of a transition time for the ATP," Shapovalov said, "but I think there is a lot of talent coming up."
His next opponent is No. 12 Pablo Carreno Busta, the highest-seeded man remaining in that half. The Spaniard earned a spot in the U.S. Open's fourth round for the first time by easily eliminating Nicolas Mahut 6-3, 6-4, 6-3. Carreno Busta will be the first man at any Grand Slam tournament in the Open era, which began in 1968, to face four qualifiers.
No. 17 seed Sam Querrey is the only American man left after beating Radu Albot of Moldova in four sets. He will face No.23 Mischa Zverev, who eliminated 10th-seeded John Isner 6-4, 6-3, 7-6 (5) on Friday night. Maria Sharapova then continued her successful return to Grand Slam tennis by beating 139th-ranked U.S. wild-card entry Sofia Kenin 7-5, 6-2 to reach the fourth round.
Shapovalov is an up-and-coming player who won the Wimbledon junior title just last year. He made his Grand Slam main-draw debut there this July, losing in the first round, but has taken significant strides since.
At Montreal last month, he became the youngest man ever to reach the semifinals at a Masters event, and he grabbed attention this week by knocking off No. 8 seed Jo-Wilfried Tsonga, a finalist at the 2008 Australian Open.
"The month of August," Shapovalov said, "has been absolutely life-changing for me."
He is a crowd-pleaser, someone who plays a fluid, an aggressive game featuring a big lefty forehand and a one-handed backhand — and he shows plenty of emotion while he's at it. He also plays wearing a baseball cap with its band tightened to an extreme degree, drawing plenty of attention on social media.
"I have a small head," he said with a smile. "It's just kind of become a little bit of my trademark."
Women's winners Friday included No. 3 Garbine Muguruza and No. 13 Petra Kvitova, a pair of Wimbledon champions who will meet in the fourth round. Also advancing were Venus Williams and Sloane Stephens, who is coming back from left foot surgery in January and is back in the fourth round in New York for the first time since 2013.