In the trophy battle, Mertens will play the unseeded Kaia Kanepi on Sunday. Kanepi took down Ekaterina Alexandrova in straight sets to advance into her first WTA final since 2013.
Osaka defeated Irina-Camelia Begu 7-5, 6-1 in an hour and 16 minutes in the quarter-final. The Japanese fired seven aces and fended off two of three break chances to mount the pressure on her opponent. Struggling on the second serve, Begu lost serve four times, fighting hard in the opener before losing ground in set number two to push Osaka over the top. Osaka plays against Anastasia Pavlyuchenkova in the Australian Open first round.
"Sorry to Tennis Australia and the fans to have to withdraw today. I have a niggling injury, and in light of the Australian Open on the horizon, I need to be cautious. I look forward to competing next week," Naomi Osaka said.