Gauff's second win over Swiatek in 13 meetings on Tuesday leaves the 20-year-old American unbeaten in the orange round-robin group, having defeated fellow US player Jessica Pegula in her previous contest.
French Open champion Swiatek lost in the US Open quarter-finals in September and was leapfrogged in the world rankings by Sabalenka after she skipped the WTA Tour's Asian swing due to fatigue.Â
Coco Gauff ensured Sabalenka would be the end-of-year No.1 with her win over Iga Swiatek. (AP PHOTO)
Now her loss guarantees that the Belarusian will end a year in which she won both the Australian and US Open titles atop the rankings.
Gauff has continued her fine form, having secured the title at the China Open in Beijing and reached the semi-finals in Wuhan.
Swiatek had dominated Gauff in their previous meetings, but the 23-year-old Pole looked rusty on her return after a two-month layoff, struggling to secure a comeback win over Barbora Krejcikova in her opening match in Riyadh.
Swiatek can now only qualify for the semi-finals if she beats Pegula and Gauff also defeats Krejcikova on Thursday.
Wimbledon champion Krejcikova's 6-3 6-3 win against Pegula earlier on Tuesday ended the sixth-seeded American's chances of qualifying for the semi-finals.
Krejcikova, who retired from the Ningbo Open quarter-finals last month due to a back injury, bounced back from her opening 4-6 7-5 6-2 loss to Swiatek in the orange group to keep her hopes of reaching the final-four alive.
"I was fighting for every ball and knew I had to play my best tennis. So, I was trying to play that and be really solid to put as many balls to the other side as I could," Krejcikova said on court.
Pegula suffered her second straight-sets defeat of the week and will play her final round-robin match against Swiatek on Thursday.
