It may be that the story that people tell of Juan Martín del Potro’s 7–5, 3–6, 7–6 (8), 6–4 win over Roger Federer in the quarter-finals of the U.S. Open is of what now will not happen, rather than what just did. Federer will not face Rafael Nadal, in what would have been their first meeting in Flushing Meadows. The No. 1 ranking will not be on the line. There will be no rematch of the Australian Open final, no contest between the man who won every set on the way to the French Open title against the man who won every set on the way to the Wimbledon crown. No thirty-eighth meeting between the greatest player of all time and the other greatest player of all time. It may be that the story is that Federer is gone, not that del Potro moves on. But, if that’s the case, we are poor storytellers, or else we are blind.

There was a man across the net from Federer, the man who will face Nadal tomorrow. Del Potro is already a U.S. Open champion himself, having won the tournament in 2009, beating Federer, in that case, in a four-hour final. That was before his injuries and surgeries, his long absences from the game. His left wrist is now more or less a tangle of fraying twine. The injuries robbed him of his backhand, which had once produced winners; he now almost always uses a neutralizing slice. It seemed to take away his chance to challenge for the majors, too, which had seemed inevitable when he overpowered Federer eight years ago. Del Potro became a great “what if” of tennis, beloved for his personality but mourned for his lost potential. His story was also of what he didn’t do, not what he did. But that turned out to be the wrong story, too.

Because on Wednesday night we saw what del Potro can still do: at 5–5 in the first set, with Federer serving at 30–15, del Potro whipped a 100-m.p.h. forehand up the line that so startled Federer that he looked staggered, as if the blow had been not to the ball but to himself; he still seemed to be reeling when he double-faulted on the next point. Later in the match, Federer had to actually duck awkwardly, thrusting up his racquet more as a shield than a weapon, as a forehand rifled by his head at net, so lethal was del Potro’s shot.

What was just as shocking was the cheer that went up from the crowd. I am not sure I can think of another match at the U.S. Open when Federer looked vulnerable and the crowd was not aggressively on his side. But this night, the olés, mostly from the upper deck, washed over the RF caps below. When del Potro did something truly extraordinary, the celebration was almost general. And del Potro did extraordinary things all night.

There is something about the Argentine that I find irresistible. No player can hit more dangerous shots—and yet he has a gentle aura to him, an air of generosity and reciprocity. Shaggy and tall, with a long face and sad eyes, he has the kind of smile that invites you to smile, the kind of head-back roar of delight that makes you want to shout. When he cries on the court, which is often, I get emotional, too.

Afterward, Federer gave del Potro all the credit. Del Potro was good; Federer was not. It was better, Federer added, that del Potro won, because the Argentine can keep winning. Federer knew that, this time, he could not. “When I walked off the court, I was, like, ‘Finally, I can rest,’ ” Federer said. “Because I’m tired.”

Federer will rest, and we’ll see him again. In the meantime, we should look ahead and not behind. Del Potro moves on. Tennis is just fine.