The tall American was given a walkover to the final after her compatriot, fifth seed Jamie Hampton, was forced to withdraw from their semi-final after suffering a right hip injury in practice.
The Australian Open, the first major of the year, starts in Melbourne on January 13.
Ivanovic, also a former world number one and 2008 French Open champion, stormed through the opening set against third seed Flipkens without dropping a game but the Belgian took her all the way in the second.
The 26-year-old prevailed in the tiebreaker, though, to win through 60 76(3) and inch closer to a first WTA title since winning in Bali at the end of 2011.
But 33-year-old Williams, a seven-times grand slam singles champion, holds an eight-one record over Ivanovic in past matches and will be aiming for her 45th WTA singles title and first since Luxembourg at the end of 2012.


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