Simona Halep became the first player to secure a spot in the 2018 WTA Finals after her triumph in the Rogers Cup final.
The world number one, who overcame Sloane Stephens in a repeat of the French Open final, booked her place as one of eight competitors in Singapore.
Halep failed to get out of the group at last year's event, but will be fancied to prevail this time around.
The only change in the top eight saw Elise Mertens climb into the reckoning, replacing former rankings leader Karolina Pliskova.
Mertens, a semi-finalist in Montreal, did not qualify for the 2017 Finals.
The other six players in the top eight are Angelique Kerber, reigning champion Caroline Wozniacki, Petra Kvitova, Elina Svitolina, Stephens and Daria Kasatkina.
