Williams, who won the pair's thrilling battle at Flushing Meadows 7-5 in the third set last month, is seeded third for the tournament in Istanbul. World number one Azarenka is the top seed.
The duo are joined in the Red Group by Germany's Angelique Kerber and China's Li Na.
The other, White, group is headed by French Open champion Maria Sharapova.
It also features the defending champion Petra Kvitova, Wimbledon runner-up Agnieszka Radwanska and French Open finalist Sara Errani.
The top two in each group progress to the semi-finals.
The action gets under way on Tuesday.