Jankovic, the tournament's seventh-seeded player, was leading 6-1, 3-0 when the match was stopped.
With the top six seeds all out of the tournament, Jankovic is the highest seeded player still in the $2 million tournament.
"I don't really think about that," Jankovic said. "I just think about my game and what I have to do on the court. I don't want to put too much pressure on myself."
Former World No. 1 Jankovic will meet France's Marion Bartoli in the quarterfinals on Thursday.
Bartoli, seeded 14th, recovered from a set down to defeat Anastasia Pavlyuchenkova of Russia, 4-6, 6-2, 7-5.
Jankovic has lost to Bartoli twice this year, at the Australian Open and at Stanford.
Top-ranked Dinara Safina of Russia, Venus Williams and French Open champion Svetlana Kuznetsova all lost their opening matches Monday after first-round byes.
Former world number one Maria Sharapova, 25th in the world following shoulder surgery last October, played compatriot Alisa Kleybanova later on Wednesday.