Jankovic, carrying the No. 2 ranking, was ousted by fifth-seeded Svetlana Kuznetsova, 2-6, 7-5, 7-5, while qualifier Katarina Srebotnik swept past Dementieva, ranked fourth, 6-3, 6-4, in Friday's quarterfinals at the Tier I hard-court tournament. A third upset of the day occurred when Nadia Petrova beat sixth-seeded Agnieszka Radwanska, 6-3, 6-0.
Only fourth-seeded Dinara Safina escaped the upset bug, although she needed three sets and more than 2 1/2 hours in topping Kaia Kanepi, 6-4, 6-7 (5-7), 6-2.
Jankovic's match took nearly as long as neither she nor Kuznetsova could grab a clear advantage. Kuznetsova took the match by breaking Jankovic's serve four of six times in the final set.
Saturday's semifinals pairs Kuznetsova against Srebotnik, who won two of the three meetings between the two, and Safina versus Petrova, who is 5-0 lifetime against Safina.
The Pan Pacific Open title, to be decided Sunday, is worth $196,900 to the winner.