Tennis, like every sport, has its what-ifs, and there is no bigger one in the men’s game in this century than: What if Juan Martín del Potro’s career had not been marred by injury after injury? Or, put it this way: If his left wrist, critical to a right-hander’s two-handed backhand, had not suffered numerous injuries—eventually requiring two surgeries that would sideline him for most of two seasons, and reduce him to chipping compromised backhands for years—would he have been as great a rival of Roger Federer’s as Rafael Nadal has been? After all, it was del Potro, then only twenty, who upset Federer in a brawl of a five-set match to win the U.S. Open, in 2009. At that point, only Nadal had beaten Federer in a Grand Slam. And here was a young player who could match flat, penetrating forehands and big serves with Fed. Nadal challenged Federer with loads of topspin; Novak Djokovic, later, with lateral defense. Not del Potro: his game, like Federer’s, was built on power and aggression. Boom—what a matchup!

Despite a few memorable contests here and there, theirs was a rivalry that never really was. Or maybe that’s not right; maybe it was just put on hold for nearly a decade. On Sunday, del Potro, now twenty-nine, defeated the thirty-six-year-old Federer 6-4, 6-7 (8), 7-6 (2) to win the BNP Paribas Open final, in the most riveting men’s match of the young 2018 season. It was never, until the very end, anything but fiercely close. It lasted nearly three high-sun afternoon hours, and followed a women’s final—won by the Japanese phenom Naomi Osaka—and championship ceremony, but no one in the Indian Wells Tennis Garden’s packed-to-the-top-rows Stadium 1 (the world’s second-largest tennis venue, after Arthur Ashe Stadium, in Flushing, New York) was inclined to leave. It was one take-that slap forehand after another. It got testy. It had one ending, then—no!—another, then still another. It felt like a rivalry.

In the first set, the two traded service holds until the fifth game, when Federer badly botched two forehands and found himself broken at love. He’d been looking to hit his shots to del Potro’s backhand in both cases, as he would the entire match, but del Potro hits his forehands with such depth and ferocity—a few of them topped a hundred miles per hour—that Federer had a hard time changing their direction. It was remarkable that Federer got so many of them back at all. He stood his ground on the baseline, as is his wont, anticipating, taking quick first steps, absorbing the pace on the short hop, and sending balls back at breakneck speed. He shanked a few, but not many. I watched the match with Christopher Clarey, of the Times, dean of this era’s tennis writers, and at one point he turned to me and said, “Age doesn’t seem to affect reaction time. Goalkeepers. Federer. Leg speed, yes, but not reaction time.”

That said, Federer never got a break-point opportunity of his own in the first set, and it was over in a little more than a half hour, ending with three love holds: del Potro, 6-4. Federer saved two break points in the first game of the second set, del Potro saved two in the tenth game, and in between there were any number of mesmerizing points—such as the second game’s second point, which reached its conclusion with a deft Federer lob that was run down by del Potro and returned with a tweener that, in turn, Federer met at the net with a put-away volley.

When a love hold by del Potro in the twelfth game brought the set to a tiebreak, things started to get a little petulant—as, strangely, they have a way of getting when these two go at it, despite how gentlemanly they otherwise tend to be on court. Del Potro began moaning to the chair umpire, Fergus Murphy, about Fed fans yelling during his service motion. (They were also cheering any time he netted a serve.) Then, when del Potro served an ace to bring the tiebreak score to 3-3, Federer began barking at Murphy for not seeing that the ball was clearly out, and then made a sweeping circle with his racquet a few inches behind the service line, where he was certain the ball had landed. Federer eventually made a formal challenge, and Hawk-Eye showed that the ball was clearly in. Fed kept grousing anyway. Del Potro did, too; things were tense. Only on the seventh set point that he had in the tiebreak did Federer convert, and the match went to a third, deciding set.

Service holds came fast and rather easily at first, but, with del Potro serving at 4-4, Federer worked things to deuce, and broke with a short backhand that del Potro could not dig out. And, in the next game, when Federer went up 40-15 on an ace and had two championship points on his racquet, things looked to be over. But, after a winner from del Potro and two unforced errors from Fed, suddenly del Potro had a break point. Then—bang, bang—Fed had another championship point. But no, del Potro passed him, and, two points later, on a blistering forehand, broke back. They eventually played one more tiebreak, and, for the first time in the match, the level of play dropped—Federer’s anyway. His serve abandoned him, and with it, it seemed, went his confidence. A last Fed forehand sailed long, and del Potro spread his arms and lifted his gaze to the blue sky. He’d won eleven matches and two tournaments in a row. Federer had lost his first match of the year. It had been a final between the two men playing best on the tour just now, and it delivered drama and also wicked power tennis.

With Andy Murray recovering from hip surgery, and out until the summer; with Djokovic and Stan Wawrinka recovering from elbow and knee surgery, respectively; with Nadal sidelined with a hip injury; with neither Sascha Zverev nor any other emerging star raising his game, why not the resumption of a rivalry that should have been? Fed vs. Delpo. Better late—quite late—than never.