Williams gained her 12th WTA finals appearance of 2013 with a 6-2, 6-2 victory over world No. 3 Agnieszka Radwanska. Williams lost only 14 points over her eight games serving and saved the only break point Radwanska managed.
She also won more than half (26-of-51) of the points when Radwanska served. Williams posted a pair of breaks in each set.
Jankovic was a 6-7 (7-9), 6-1, 6-1 winner over ninth-seeded Petra Kvitova in her semifinal. After the tight first set -- Kvitova won two more points than Jankovic in the set -- Jankovic took more than two-thirds of the points in the second and third sets.
Jankovic was ranked No. 1 for 18 weeks in 2008 and is currently 11th.
Williams is 6-4 all-time versus Jankovic and needed three sets to win the title match at Charleston, S.C., in their only meeting this year.
Williams is 9-2 in WTA finals this year and 55-17 all-time in championship matches. Jankovic is in her third title match of 2013. She won in Colombia before the loss to Williams in South Carolina. Jankovic is 13-17 in title matches.
The winner of Sunday's Jankovic-Williams match will collect $860,000 with the runner-up check worth $430,365. Radwanska and Kvitova were each given $210,000 for making the semifinals.