In a grand five-set opening for the Grandstand, John Isner caught Frances Tiafoe at the finish line

NEW YORK—Frances Tiafoe had been the better player for three sets against John Isner. Now, at 5-5 in the third-set tiebreaker, the 18-year-old found himself two points from upsetting the U.S. No. 1 and recording the biggest win of his young career. Tiafoe had just snapped off a crosscourt forehand winner, and as he moved forward to take a floating shot from Isner, he looked poised to do the same from the backhand side. The crowd in the brand-new Grandstand court at Flushing Meadows was poised, too. They had been forced to choose between two Americans in this match, and they had sided with the teenager, chanting his name throughout.

From the start, the College Park, MD., native had responded. In the second game, Tiafoe had ambushed his countryman by reaching up to reflex an Isner overhead back down the line for a winner, bringing the audience to its feet. After that, the speedy Tiafoe was off to the races, both with his feet and his racquet. He timed Isner’s first serves and sent them rocketing back for return winners. He surprised his long-limbed opponent with the raw pace and funky, unorthodox delivery of his ground strokes; Tiafoe’s shots were on Isner’s racquet before he had time to react. After Tiafoe blitzed through the first two sets, 6-3, 6-4, many of us waited for the inevitable collapse in the third, but it didn't come. Isner had found his timing, but Tiafoe had hung tough enough to take it to a tiebreaker.

At 5-5 in the breaker, though, Tiafoe tried to do something different. He tried to do something more. For three sets, he had beaten Isner with pace, without needing to hit the ball close to the lines. He had taken, as Paul Annacone likes to say, “aggressive cuts to conservative targets,” and it had worked. This time, though, Tiafoe did aim the for the line with his backhand. And he missed it.

This was one of those moments that, despite the fact that one player is well ahead on the scoreboard, can feel like a co-match point. The underdog has worked his way to the brink of victory, but the veteran has stayed just close enough to keep him nervous. In these cases, the underdog needs to cross the finish line in his first attempt, because it’s only going to get harder from there; if he loses the third set, he has to start all over in the fourth. In that sense, Tiafoe-Isner reminded me of this year’s Wimbledon quarterfinal between Roger Federer and Marin Cilic. Like Cilic that day, Tiafoe did everything except come up with the one shot he needed to end it. But that’s what tennis’ scoring system demands. Tiafoe won one more point than Isner (149 to 148), but Isner won one more set, 3-6, 4-6, 7-6 (5), 6-2, 7-6 (3).

While this match began by showing us what the teenage Tiafoe is capable of, it ended by showing us what has made the 31-year-old Isner such a flinty, and underrated, competitor for so long. It’s rare that you see Isner get off to such a slow start, or play so poorly for two full sets, against a lower-ranked opponent. Despite being the second-best player on the court for the better part of three-and-a-half hours, Isner kept holding serve, and he clawed his way back from 1-3 down in the third-set tiebreaker.

When Tiafoe served for the match at 5-3 in the fifth set, Isner played his best and savviest game of the match. After spending much of that set at the baseline, he went on the attack. And after failing to make any inroads on Tiafoe’s serve, Isner came up with the returns he needed. The same was true in the fifth-set tiebreaker. On the first point, Isner ran around a Tiafoe serve, jumped on a forehand and jumped out to a 1-0 lead that quickly expanded.

“I just tried to play solid,” Isner said of his fifth-set comeback. “I came up with the returns I needed, and I was a little lucky.”

Isner was referring to a forehand that Tiafoe missed when he was serving for the match at 5-3. After going down 0-40, he had fought back to 30-40; but sticking with the theme of his day, he came up one shot short. Tiafoe lined up an inside-out forehand that looked sure to be a winner, but he hesitated for a split second and hit it into the tape. Tiafoe hit 44 winners, but he needed one more.

Afterward, the two players hugged, and Tiafoe buried his face in Isner’s shoulder. Tiafoe recovered enough to show his appreciation for the crowd, the match and the moment.

“Thanks for making this unbelievably fun,” he said, showing a remarkable amount of perspective for an 18-year-old after such a crushing defeat.

“He’s a class act,” Isner said of Tiafoe, who made himself a lot of new fans today.

But Isner’s performance was first class, too. Hopefully, the people who cheered on Tiafoe can appreciate what Isner had to do to beat him.

Two Americans, two generations and two performances worth applauding, with a hug as the curtain came down: It was a grand opening for the Grandstand.