Félix Auger-Aliassime is the other Canadian tennis phenom—the one not named Denis Shapovalov. He’s been a phenom for a while. He won three titles at the Challenger and Futures levels, the men’s tour’s minor leagues, before he turned seventeen. (Novak Djokovic did that, and Juan Martín del Potro did that, and Richard Gasquet did that—but nobody else has.) At seventeen, he became the youngest player to break into the A.T.P. top two hundred since Rafael Nadal did it, in 2002. Now, at eighteen, Auger-Aliassime (that’s oh-jshay ahl-ee-ah-seem) is the youngest player in the top hundred on the men’s tour. And, on Saturday, in the biggest win of his young career, he defeated the twenty-year-old Stefanos Tsitsipas, the rising star from Greece with the Borg-like tangle of sun-bleached hair, in straight, efficient sets, 6–4, 6–2.

As the name and its pronunciation suggest, Auger-Aliassime is French-Canadian. He grew up in L’Ancienne-Lorette, a suburb of Quebec City. His mother is Québécoise; his father, a tennis coach who began training Félix at age four, immigrated to Canada from Togo. Canada’s recent success in men’s tennis owes something to its welcoming immigration policies. Milos Raonic, the highest-ranking men’s singles player in Canadian history, is the son of Serbian engineers. The parents of Vasek Pospisil, who reached the top five in doubles in 2015, fled Communist Czechoslovakia for Austria before making their way to Canada, in 1989. Denis Shapovalov’s mother, who had played for the national team of the Soviet Union, arrived in Canada with baby Denis, his older brother, and her husband, from Tel Aviv.

I got my first glimpse of Auger-Aliassime last August, at the U.S. Open. He’d made his way through several days of qualifiers to earn a spot in the main draw, and, in the first round, he drew Shapovalov. It was tied a set apiece when I got there, and, even as night fell, the Flushing air remained close and near simmer. Two games into the third set, Auger-Aliassime lay down on the court and signalled for a trainer. He felt faint, it turned out, and couldn’t stop his heart from racing. He soon enough retired, sobbing at the net on Shapo’s shoulder.

Since then, Auger-Aliassime’s been on a tear. In October, he won a Challenger tourney, in Uzbekistan (such is minor-league tennis), and he began this year by reaching the final of an A.T.P. five-hundred-level tournament—the youngest player to ever accomplish that—in Rio.

Tsitsipas had been playing some remarkable tennis of his own lately. He reached the semifinals of the Australian Open, defeating Roger Federer along the way. He won an indoor tournament in Marseille without dropping a set, then reached the final of the Dubai Tennis Championships, where he lost to Federer. (Nobody beats even an aging Federer twice in two months.) He arrived at Indian Wells having cracked the top ten.

Auger-Aliassime had beaten Tsitsipas three times in three tries at the junior level; perhaps that explains the calm confidence that Auger-Aliassime exhibited from the very start of the match. And, after those deep runs in Melbourne, Marseille, and Dubai, maybe Tsitsipas had just played too much tennis—too much for a young player, anyway—in too short a time. (“I feel like I had enough of tennis already,” Tsitsipas said after the match, after noting that his “mind at the moment is not very fresh.”) Many of the fans on hand seemed to be Canadian snowbirds, wintering in the California desert; they were loudly urging Auger-Aliassime on from the very start, in the complex’s cavernous Stadium 1. They may have had something to do with the result, too.

Mostly, though, Auger-Aliassime, as he often does, managed to play a very big game and a surprisingly clean game at once. Considering the huge cuts that he takes at the ball, especially with his serve and forehand, he made relatively few errors. His approach is what coaches refer to as “first strike” or “serve plus one”: deliver a crushing first serve, which forces your opponent to offer a weak return, which you can then take with your forehand and pummel for an angled winner, to one corner or the other. His first serve seldom arrived at less than a hundred and twenty-five miles per hour. Tsitsipas set up for it four or five feet behind the baseline, to try to counteract the high bounce that the ball was taking off the gritty hard courts in the thin desert air, but he couldn’t generate much depth from back there. His returns were often too short, when they made it over the net at all. (He had six break-point opportunities in the fourth game of the match and couldn’t convert any of them.) And his return strategy left a lot of space in front of him, which Auger-Aliassime used, hitting resounding, third-shot forehands at acute angles. One of them, which he sent in Tsitsipas’s direction with a thunderous thwock, was clocked at more than a hundred miles per hour, before it bounced off the wall near the court’s entrance tunnel. That was the penultimate point of the match. Auger-Aliassime sealed his victory with a serve that never came back.

Auger-Aliassime is six feet three. His high fade makes him seem even taller, and, if it’s possible, younger. He is delicately handsome, and, as he spoke with reporters after the match, his voice was soft, his smile easy and wide. Still, he was firm enough about the tennis he had played. “I was able to be pretty aggressive,” he said. “That’s my style of play. . . . I try to impose myself.”