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Pegula dialled up the intensity after an early exchange of breaks in the opening set, as the 2023 runner-up eased to a 4-2 lead when Rybakina appeared to struggle with accuracy because of a shoulder issue sustained during her warm-up a day earlier.

"It was such a tough battle. It's always difficult to play against Jessica and she started pretty well," Rybakina said.

"It was very quick, she broke me and it wasn't easy to come back. I'm glad I managed to find my way in the second and win it in a three-set battle."

The 31-year-old Pegula promptly closed out the first stanza thanks to Rybakina's 25th unforced error, but there was a sudden shift in momentum in the next set as she found herself 1-4 behind and in danger of being dragged the distance.

Pegula recovered her rhythm and pushed hard in her bid to draw level in the set, but Rybakina responded fiercely in the 10th game to force a decider, where the pair swapped breaks again in a tight battle.

A forehand into the net from Pegula at the end of the eighth game handed the advantage back to Rybakina, who remained calm to hold in the next game and secure the victory that maintained her perfect record in the season finale.

"My serve helped me when I needed it," Rybakina, who sent down 15 aces, said.

"I was trying to stay focused on each point when we had some tough rallies. In the end I managed to push myself a bit more."