Daria Kasatkina upset Venus Williams 4-6, 6-4, 7-5 in a nearly three-hour baseline struggle and Naomi Osaka routed top-ranked Simona Halep 6-3, 6-0 in 64 minutes on Friday night to set up a final between two 20-year-olds. “We are coming,” Kasatkina said, smiling. “Very soon.”

Osaka put away Halep on her third match point when the Romanian netted a backhand. “Both of them deserve to be in the final,” Halep said. Ranked 44th, the Japan-born Osaka opened the tournament by beating Maria Sharapova in the first round. She defeated No. 31 Agnieszka Radwanska and No. 5 Karolina Pliskova on her way to the final, dropping just one set in six matches.

Kasatkina was two points from defeat, trailing 4-5 and 0-30 in the third set when Williams committed four straight errors as the Russian tied it 5-all. Williams won just two more points as Kasatkina took the last two games to close out the match in 2 hours, 48 minutes. Kasatkina dropped her racket near the baseline and covered her face with her hands as she walked to the net.

Kasatkina has defeated four top-20 opponents at the same tournament for the first time in her career. She owns wins over all four current Grand Slam titleholders in the last year. A victory in Sunday’s final would move her into the top 10. After shaking hands, Kasatkina pumped her fists and shook her head slightly as if in disbelief at beating the 37-year-old American and advancing to the biggest final of her young career.