PARIS — Before there was Carlos, there was Félix.

It is not so easy to recall now, through the haze of the pandemic and the aftershocks of Carlos Alcaraz’s meteoric impact on tennis of late. But there was a time, beginning in roughly 2015, that the tennis cognoscenti raved about a young Canadian named Félix Auger-Aliassime, calling him a potential heir to Roger Federer, Rafael Nadal and Novak Djokovic.

After a quality start to the year but a rocky late winter and spring for Auger-Aliassime, that concept never felt farther away than during his first two sets of the French Open on Sunday. Auger-Aliassime came out flat and wild for the first men’s match on the main stadium court. For 88 minutes he was lost against little-known Juan Pablo Varillas of Peru, 25, who is ranked 122nd and had his opponent complaining to himself and anyone else who would listen.

Then, with a few flicks of his forehand, a few blasted serves and some deft drop shots, Auger-Aliassime was back, displaying his unique mix of power, precision, touch and speed. He prevailed, 2-6, 2-6, 6-1, 6-3, 6-3, in a 3-hour-14-minute scare that made for a very Félix-like afternoon.

Auger-Aliassime made the final of the Roland Garros junior tournament in 2016, at age 15, and then won the U.S. Open boys’ title later that year. He was 6 feet 2 inches (on his way to 6-4), with long arms and fast feet. He could switch directions like a wide receiver. He had broad shoulders that left plenty of room for his torso to fill out and add even more power.

He was also polite and courtly, approaching the game with a humility that coaches said drove him to train hard every day. Watching him play a match in his teenage years, Gastão Elias, a longtime Portuguese pro, said Auger-Aliassime “has been an adult since he was 12.”

Auger-Aliassime may one day fulfill all the promise of his teenage years. He is just 21, ranked ninth in the world and the youngest member of the top 10 not named Alcaraz. But if he does, the journey will have involved plenty of fits and starts, including losses in his first eight finals and other moments when he seemed about to take off only to fall flat.

And now, as he strives to reach the level of the Big Three — along with Stefanos Tsitsipas, Alexander Zverev and so many others — there is Alcaraz to contend with, a 19-year-old charging from the rear, piling up trophies and wins against the game’s greats and making that last, hardest step look easy. In mere months, Alcaraz has changed the calculus for all the 20-somethings, though Auger-Aliassime’s bigger problem of late is inconsistency, not Alcaraz.

“Before, it was just Nadal and Federer and Djokovic,” said Louis Borfiga, a longtime French tennis teacher and the architect of Canada’s modern tennis development machine. “Now there is an incredible player coming. He has to work very hard, and he has to stay positive, to believe in himself and his game.”

Auger-Aliassime has no illusions about the difficulty of what lies ahead.

“The toughest part is always what’s ahead of you, isn’t it?” he said one afternoon last month in Portugal, before being upset in a quarterfinal at a small tournament in which he was the top seed. “What you haven’t done before.”

If he can take the final step, Auger-Aliassime could be the sport’s perfect celebrity, a multiracial star with roots on three continents. He grew up in the largely French-speaking province of Quebec, the son of an immigrant from Togo, where he donates hundreds of thousands of dollars each year to children’s causes.

He has since moved to Monaco and spends plenty of time in France and Spain, making him a new favorite in Europe.

“Allez Félix!” the fans yelled on Sunday as he tried to come back in his match.

And the proximity of his childhood to New York, among his other attributes, has endeared him to the U.S. Open crowd, earning him an invitation to last year’s Met Gala, where he wore a white dinner jacket on the red carpet.

“We still have borders, but I consider myself a citizen of the world,” he said.

Auger-Aliassime was as good as anyone in the world in the first six weeks of the year, leading Canada to the championship of the ATP Cup, getting to match point against Daniil Medvedev (the eventual finalist) in the Australian Open quarters, then seemingly breaking through by winning the Rotterdam Open, his first title.

Nadal and Federer are invested in his success. Auger-Aliassime occasionally trains at Nadal’s academy in Majorca, working with Nadal’s uncle and former coach, Toni Nadal. Federer texted Auger-Aliassime in February when he finally won his first tournament. “I’m happy for you, well done,” Federer wrote.

But more downs than ups have followed, with early losses on hardcourts, which are supposed to be his best surface, and then on clay in Marrakesh, Monte Carlo and Estoril, Portugal, where he was the top seed.

“After January, we did not expect the losses, but we know consistency is very difficult,” said Frédéric Fontang, Auger-Aliassime’s coach since 2017. “He does have an ability to absorb and keep learning and always do his best, and that is the first talent that a top player must have.”

This is the way it has always been for Auger-Aliassime, ever since his father, Sam Aliassime, a tennis coach in Quebec, introduced him to the sport when he was a boy. Aliassime coached his son until he was 13. Auger-Aliassime then moved to Montreal to train with Canada’s suddenly vibrant development program.

Borfiga first saw Auger-Aliassime play as a 6-year-old, but it was four years later that his potential became apparent. Borfiga said he already had a “heavy ball,” a term tennis coaches and players use to describe someone whose strokes naturally produce shots that mix power and spin in a way that makes them difficult to return.

Auger-Aliassime said he began to grasp how good he might one day be when he won an international junior tournament in Auray, France, when he was 11.

“From then on, the belief was there,” he said.

His success and personal appeal have attracted plenty of blue-chip endorsements, including a partnership with BNP Paribas, the international bank that is among the biggest sponsors in tennis. For every point Auger-Aliassime wins on tour this year, the bank donates $15 and Auger-Aliassime donates $5 to children’s education in Togo.

“He represents the youth,” Jean-Yves Fillion, the chief executive of BNP Paribas USA, said of Auger-Aliassime.

And yet there are those vexing defeats — coughing up a two-set lead to the Russian qualifier Aslan Karatsev at the 2021 Australian Open; an early loss to Max Purcell, the 190th-ranked player, at the Tokyo Olympics; and a second-round loss at the 2021 National Bank Open on home soil in Toronto to Dusan Lajovic of Serbia. And then there was Sunday’s nervy escape during his first appearance on Philippe Chatrier Court.

Auger-Aliassime’s team, led by Fontang, built his schedule in 2022 around opportunities for victories, including more smaller tournaments. If he can start winning those, then maybe winning will become a habit.

Fontang said players with an aggressive style like Auger-Aliassime’s might take longer to reach their full potential because they were more prone to mistakes, though few players are more aggressive than Alcaraz. He said Auger-Aliassime’s physical gifts made his success nearly inevitable in his mind. But Fontang wants Auger-Aliassime to be even more aggressive, to take advantage of his power and size by coming to the net more and finishing points, though that could hasten further inconsistency.

“Of course, the future we cannot know, but he just can’t be static,” Fontang said. “What you see with the best players is that there is no part when they are standing still.”

Auger-Aliassime has no intention of doing that, even though he knows the path to the top keeps getting narrower the higher he climbs. Tennis math, simple as it is, is exceedingly cruel. There are only 10 players in the top 10, and only one can be No. 1.

“The elite,” he said with a shake of his head, “are just so consistent.”