Swiatek is the only major singles champion at the WTA FinalsWorld number one Iga Swiatek has claimed a semi-final spot at the WTA Finals with a straight-set win over France's Caroline Garcia.
Poland's Swiatek won 6-3 6-2 in Texas.
However, Garcia can still reach the knockout stage with a win on Saturday against Daria Kasatkina, who put American Coco Gauff out of semi-final contention with a 7-6 (8-6) 6-3 win.
"It's the last tournament of the season, so I have kind of nothing to lose," Swiatek said.
"I don't have to worry what I'm going to do next. For sure, I'm giving it 100%, physically and mentally."
Swiatek's victory means she is the second player, after Greek world number five Maria Sakkari, to guarantee her progress from the round-robin stage of the season-ending event in Fort Worth.
It is the Pole's 47th straight-set win this year on the tour.
The 21-year-old US and French Open champion saved five of the six break points she faced and broke Garcia four times to sit top of the Tracy Austin group, while Gauff's defeat by Kasatkina left her bottom of the group.
World number four Gauff, who, along with Kasatkina, is making her debut at the WTA Finals, was undone by 43 unforced errors compared with the Russian's 14.
"It was tough," Kasatkina, eighth in the WTA rankings, said.
"I was nervous at the beginning. With the rhythm of the match, nerves disappear a little bit and start to be better.
"So I'm really happy to be still alive."
On Friday, Ons Jabeur, Aryna Sabalenka and Jessica Pegula will try to join Sakkari in qualifying from the Nancy Richey group.
Jabeur and Sabalenka both have a 1-1 record while Pegula could still progress despite losing both of her singles matches so far.
American Pegula plays Belarusian Sabalenka before Tunisia's Jabeur faces Sakkari.
The tournament, featuring the eight best players of the year, was moved from usual host city Shenzhen for the second successive year following the WTA's suspension of all tournaments in China amid concern for Chinese tennis player Peng Shuai.
