Montreal's Eugenie Bouchard will try to continue her string of big wins at the Pan Pacific Open when she faces American star Venus Williams in the quarter-finals.

Bouchard upset sixth-seeded Jelena Jankovic of Serbia 7-5, 6-2 on Wednesday, a day after ousting No. 8 Sloane Stephens of the U.S.

Bouchard, making her debut in the Tokyo tournament, broke Jankovic to go up 5-2 in the second set and then held serve to win the match in 1 hour 10 minutes at Ariake Colosseum.

'I felt like I wasn't playing my best in the first set. But I ... started to get a lot more aggressive near the end of the first set and that was the turning point.' - Eugenie Bouchard on Wednesday's win

Jankovic had a 5-4 lead in the first set, but Bouchard won the last three games after a talk with her coach.

"I felt like I wasn't playing my best in the first set," Bouchard said. "But I stayed with her and started to get a lot more aggressive near the end of the first set and that was the turning point."

Bouchard, who is 46th in the WTA rankings, said winning last year's junior Wimbledon title has given her confidence to compete at a higher level.

"That gave me a lot of confidence to play in the pros," Bouchard said. "Playing week in, week out against the top players has made me a better player."

Williams rallies for win

The 19-year-old Bouchard will next face Venus Williams, a 4-6, 7-5, 6-3 winner over 13th-seeded Simona Halep of Romania. 

Williams, making her first appearance in the Tokyo tournament since 2009, broke serve to lead 5-3 in the third set at Ariake Colosseum and then won with a cross-court forehand that No. 13-seeded Halep hit into the net.

"It was a very tough match," Williams said. "She played very well. I don't know how I was able to win the match. I just wanted to stay in Japan longer."

Williams, who has slipped to 63rd in the world rankings, ousted top-seeded Victoria Azarenka on Tuesday.

In other third-round matches, fourth-seeded Caroline Wozniacki defeated Magdalena Rybarikova 6-1, 6-1, and second-seeded Agnieszka Radwanska beat Dominika Cibulkova 6-3, 6-4.

Fifth-seeded Angelique Kerber of Germany overpowered No. 11-seeded Ana Ivanovic of Serbia, 6-4, 6-2, and Lucie Safarova of the Czech Republic beat No. 12-seeded Samantha Stosur of Australia, 6-4, 6-4.