DOHA, Qatar — In those early months of the season, before anything was decided, the superstars of Paris St.-Germain mostly talked about what they could win together.
The French championship was surely viewed as a formality; P.S.G. these days always seems to win that title. The Champions League was seen as a bigger prize; the team, assembled with the outlay of vast quantities of Qatar’s considerable wealth, had never won it.
But in the locker room at Paris St.-Germain’s training facility, the team’s three headliners — the star forwards Neymar of Brazil, Kylian Mbappé of France and Lionel Messi of Argentina — also had another trophy on their minds. As they exchanged gentle ribbing and regular banter inside the aging locker room at Camp des Loges, a former French military camp surrounded by forest on the outskirts of Paris, all of them knew the World Cup was coming, and all of them desperately wanted to win it.
“Everybody defends his country,” Mbappé said, laughing as he described the exchanges during an interview at The New York Times’s Manhattan office this summer. “But we laugh a lot. We’re gonna say: ‘Yeah, my country’s gonna win. We’re gonna beat you. No, we are gonna beat you.’”
But now what for months served as background chatter, a way for top athletes to blow off steam, has suddenly become very real.
Neymar has already left the conversation, and the World Cup. But Mbappé and Messi are safely through to Sunday’s final at the stadium in Lusail. Messi, who has said he is playing his final World Cup, will be seeking to claim the only prize that has eluded him in a glittering career. Mbappé is after a different honor: He can become a double World Cup winner if France wins on Sunday, repeating a feat last achieved by the Brazil teams of Pelé in 1958 and ’62.
Mbappé had already written his name alongside Pelé’s four years ago in Russia, when he joined the Brazilian as the only teenagers to score in a World Cup final. His stunning run of form then, not only the goals but the unshakable confidence he showed in helping to deliver France’s title, elevated his status to genuine superstar overnight.
In Qatar, Mbappé could no longer have the comfort of being the coming man, someone who might emerge from the shadows. Excellence, he knew, would be expected.
“It’s different because I’m a different player,” he said of his second World Cup. “When I arrived in my first World Cup, I was a young teenager. I was a young guy. Everybody in the world didn’t know me well. I was a big player of P.S.G. but not really famous around the world. Now it is different. Everybody knows me — the pressure is different.”
So far, Mbappe appears to have handled that pressure.
He and Messi are tied in the race to be the tournament’s top scorer, with five goals each. While he has not always been at his very best, including curiously quiet stretches against both England and Morocco in the knockout round, Mbappé has regularly shown glimpses of the pace and explosiveness that will leave little doubt that he carries on his shoulders France’s chances of conquering Argentina, and Messi.
“For me it is the biggest thing in world football,” Mbappé said. “Because when you talk about football, you have the World Cup in your mind. Because this is the only competition that everybody watches. You don’t need to love football to watch the World Cup.”
The mass appeal will only be heightened on Sunday. The final’s predominant story line — Messi’s final shot at the one trophy he craves more than any other — has in part cast Mbappé as a foil in the narrative, the key man who could keep Messi from getting his Hollywood ending.
The two have been teammates for more than a year now, the young contender and the aging star, and it has sometimes felt like a bumpy accommodation. As if sharing a field, let alone one ball, might not be enough to assuage the collections of talent — and egos — assembled by P.S.G., Mbappe said the noise that sometimes surrounds those relationships is not always an accurate reflection of reality.
After all, he said, like any other soccer-loving child, he would have dreamed of lining up alongside Messi and Neymar.
“I think the problem comes from outside because everybody asks questions they don’t have answers for, so they put some problem between us,” Mbappé said in the summer, amid whispers he had demanded control as the price for his re-signing with P.S.G. News reports about discord, he said, were untrue. “We have a great relationship.”
But it is hard not to see that relationship tested on Sunday. One of them will leave the field a champion, the other with his heart broken.
Mbappé said he knew what to expect. Able to study Messi’s game at such close quarters at his club for more than a year, he said that he has been in awe of the Argentine’s ability to pick the right move, to play the right pass, to measure the moments requiring his intervention with perfect timing, no matter the chaos around him.
“He is calm, always calm,” Mbappé said of Messi. “Calm with the ball. Calm before he shoots. He always has control of everything he does.
“It’s really impressive because sometimes there is big pressure with the game and with the fans, with the people. But he is always calm to make the right decision in the right moments.”
Sunday, too, may be decided in one moment, by one moment of genius from Messi or, just maybe, a winning goal from Mbappé.
Outside Al Bayt Stadium earlier this week, in the early hours as Wednesday turned into Thursday after France defeated Morocco in a semifinal match, there was a sense of relief as well as pressure in Mbappé’s camp. Fayza Lamari, his mother and a cornerstone of his relentless march to stardom from the earliest days, emerged from the arena near the V.I.P. entrance yelling, “We won! We won!” as she made her way toward the exit.
She was not the only one smiling. Qatar, which has spent more than $200 billion on staging the World Cup, now has its dream final. In a few weeks it will welcome both Messi and Mbappé to P.S.G., reuniting its two biggest stars on the Qatari-owned club after they have squared off in a showcase final in Lusail.
For Qatar, the question of Messi or Mbappé does not really matter. It has already won.
