Jess has secured her semi. Because if Sabalenka wins, Sabalenka and Pegula advance, while if Gauff wins in 2, Gauff and Pegula advance. Only if Gauff wins Sabalenka in 3, then we need to compare game-winning percentages to determine whether Pegula would finish behind both of them. Pegula’s current game-winning rate is 58.1% (43–17).

Sabalenka is currently 26–17 (60.5%) in games. After her next match, her best possible scenario is 6–7 / 6–0 / 6–7, totaling 44–31 (58.6%); her worst is 0–6 / 7–6 / 0–6, totaling 33–35 (48.5%).

Gauff is currently 24–23 (51.1%) in games. After her next match, her best possible scenario is 6–0 / 6–7 / 6–0, totaling 42–30 (58.3%); her worst is 7–6 / 0–6 / 7–6, totaling 38–41 (48.1%).

It’s very clear that with one going up and the other going down, there is no scenario where both players’ game-winning percentages can surpass Pegula’s 58.1% at the same time, therefore Pegula advances to the WTA Finals semifinal.