Winner of the US Open in 2004 and the French Open in 2009, the 34-year-old Russian has now defeated Czech third seeded Karolina Pliskova and Barty in successive matches.
Ashleigh Barty stunningly lost her chance to regain the number one world ranking when the Australian was beaten in straight sets by Russian Svetlana Kuznetsova in the semi-finals of the Cincinnati Masters on Saturday.
Top seed Barty, who would have replaced the injured Naomi Osaka as the world number one with a victory, struggled with the rhythm off her serve as she lost 6-2, 6-4, losing eight consecutive games to the Russian at one point.
Kuznetsova, ranked world number 153, will play the winner of Saturday's later semi-final between Americans Madison Keys and Sofia Kenin for the title on Sunday.
Winner of the US Open in 2004 and the French Open in 2009, the 34-year-old has struggled with injuries throughout her career but has now defeated Czech third seeded Karolina Pliskova and Barty in successive matches.
She entered the Cincinnati tournament as a wild card after earlier having issues in obtaining a US visa that kept her from defending her Washington DC title.
"Maybe one week or two weeks helped me back home," she said. "Something important happened in my life and now I feel better."
Barty won the first two games, then lost the set as Kuznetsova, handling the Australian's slices effectively and serving well, won the next six.
Barty at one point called a medical time-out to have her right ankle retaped.
But the streak continued in the second set, with Kuznetsova winning the opening two games before Barty held.
The Australian rallied to 4-3 and 5-4 before Kuznetsova served out the victory.