Top-ranked Aryna Sabalenka will try to hold off Poland's second-placed Iga Swiatek for the year-end world No 1 spot when the WTA Finals begin on Sunday in Cancun, Mexico.
The $9 million season-ending outdoor hardcourt showdown of eight top players features round-robin group matches to decide semifinal pairings ahead of the 5 November championship match.
Sabalenka, the reigning Australian Open champion, was the runner-up in last month's US Open and reached the semifinals at Wimbledon and the French Open.
The 25-year-old from Belarus also won WTA titles this year at Madrid and Adelaide and enters the WTA Finals with a 630-point lead over 22-year-old reigning French Open champion Swiatek.
Four-time Grand Slam winner Swiatek, the 2022 year-end world No 1, also took 2023 titles at Stuttgart, Qatar, Poland and earlier this month at Beijing.
Sabalenka can clinch the year-end top spot by reaching the final with a 2-1 group stage record no matter what Swiatek does.
"It's not just about becoming world No 1," Sabalenka said last month in China.
"I think it's about finishing the year as world No 1 and staying there as long as you can."
If Swiatek loses a round-robin match, Sabalenka can secure the year-end No 1 by going unbeaten in group play or reaching the final.
Should Swiatek drop two matches in the group stage, a 2-1 round-robin record would be enough to make Sabalenka the year-end rankings leader.
Swiatek, this year's WTA match wins leader with 63, must make the final to have a chance at the year-end No 1 provided Sabalenka plays all her group matches.
If Sabalenka wins even one group stage match, Swiatek would need to win the title for a chance at the throne.
Others in the field include 19-year-old US Open champion Coco Gauff, fellow American Jessica Pegula, Greece's Maria Sakkari, Ons Jabeur of Tunisia, Kazakhstan's Elena Rybakina and Czech Marketa Vondrousova, the reigning Wimbledon champion.
Sabalenka became world No 1 after her run to the US Open final in September, ending Swiatek's 75-week reign atop the rankings after reaching No 1 for the first time in April 2022.
In last year's WTA Finals, Sabalenka snapped a four-match losing streak to Swiatek with a semifinal triumph but dropped the final to France's Caroline Garcia.
In two meetings this year, both in WTA clay finals, Swiatek won at Stuttgart and Sabalenka won at Madrid.