It had taken the former top-ranked Serbian three rain-affected days to complete the victory over the 21-year-old Japanese left-hander playing her first quarterfinal in a WTA Tour event.
Jankovic says “It was really difficult, but it has been really difficult for all of us in these conditions. It was especially important to remain focused.”
Jankovic, who won here five years ago, will face Zheng Jie of China in the semis.
Former US Open quarterfinalist Melanie Oudin overcame fellow American Irina Falconi 6-4, 5-7, 7-5 and will face Ekaterina Makarova, the eighth-seeded Russian who advanced on Saturday, in the other semi.