Former world No. 1 Jankovic, seeded eighth this week, won the Beijing title in 2008 and was runner-up the previous year.
She is one of only two active players to have beaten Serena four times or more -- the older Williams sister Venus is the other.
"She's the best player in the world right now," Jankovic said of the U.S. Open champion. "She's in unbelievable form. Even though I have beaten her in the past I think she's the most difficult player to play against."