Jannik Sinner is world No. 1 again, but only for a week.

On Sunday, Sinner defeated Félix Auger-Aliassime to win the Paris Masters, an ATP 1000 competition with a grand prize of nearly $1.1 million. The win elevated Sinner above Carlos Alcaraz, who reclaimed the No. 1 spot at the US Open in September, after he lost in the Round of 32, his lone match of the tournament.

The Italian will enter the 2025 ATP Final, which starts this upcoming Sunday in his home country, as top-ranked player, but will lose it back to Alcaraz on the second day of the tournament.

Alcaraz will return to top of the rankings on Monday due tennis’ complicated scoring system, where points are determined using a 52-week period. Sinner will lose 1,500 points since he won the 2024 ATP Finals, while Alcaraz will be deducted 200 points after winning just one of three group stage matches last year.

Alcaraz will then hold a 1,050-point lead over Sinner during this year’s tournament, setting up a season finale—one that already comes with a potential record-setting prize—that will determine who finishes the year as the best men’s tennis player.

The ATP Final is different from most other tennis tournaments because it is not a knockout tournament. A player can advance past the group stage even if they lose a match.

Each win has a corresponding amount of points and prize money:

• Round-robin win: 200 points, $396,500
• Semifinal win: 400 points, $1.18 million
• Final win: 500 points, $2.37 million
• Total for an undefeated champion: 1500 points, $5.07 million*

*There is also a participation prize worth up to $331,000 for three round-robin matches.

Alcaraz has to score at least 450 points to secure the world No. 1 spot at the end of the season. That would mean either a three-game sweep in the group stage, or two group stage wins and a semifinals victory. 

Sinner would need to sweep the tournament or win all but one match to stand a chance at supplanting Alcaraz. He would need help from the rest of the eight-man field, which includes Alexander Zverev, Novak Djokovic, Ben Shelton, Taylor Fritz, and Alex de Minaur. (The last spot has yet to be determined, but is between Auger-Aliassime and Lorenzo Musetti.) 

The group is more than capable of dealing a loss to Alcaraz, especially with the Spaniard looking vulnerable following the Paris Masters.

But it’s only fitting that the 2025 season finale serves as the determinant for world No. 1, given the year was defined by Alcaraz and Sinner. The two faced-off in five tournament finals this year, including three Grand Slam final matches—the first time in history a duo played each other in three major finals in the same calendar year.

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