Osaka joined Mboko in pulling out of the main tuneup for the U.S. Open after their gripping contest in Montreal.

Osaka has made progress since returning in last year's Australian Open. She won two matches in both the Australian Open and Wimbledon this year, has earned $725,727 in prize money and reached the No. 49 spot in the WTA rankings, with a higher ranking likely on the way by making the final.

Canadian teenager Victoria Mboko completed a dream run to the National Bank Open title Thursday night, overcoming a slow and swollen right wrist start to beat Japanese star Naomi Osaka 2-6, 6-4, 6-1.