There was only one scenario by which Iga Swiatek would have finished the year as world number one, and she's close to completing it.
Before the WTA Finals started, we knew that either Iga Swiatek or Aryna Sabalenka would finish the year as world number one. Sabalenka needed a few things to go right for her, and while she did her part by making the semi-final, she failed to beat Swiatek in that semi-final.
That is the worst-case scenario for her because if she had won that match, she would have ensured that she finished as world number one. The match was postponed a few times because of rain, and that impacted Sabalenka too much.
She didn't lose the number one rank just yet because her opponent, Iga Swiatek, needed to win the final to secure the number one rank. Sabaleka has 9050 points right now, while Swiatek has 8875.
If Swiatek beats Jessica Pegula on Monday, then she'll earn enough points to overcome Sabalenka at number one. If the Polish player loses, she will ensure that Sabalenka will finish as number one, so the situation is quite fluid but rather simple for both players.
It's out of Sabalenka's control because she can't do much here; she needs to wait and see whether Jessica Pegula will do her a solid. There is a pretty good chance that she will because a big trophy is up for grabs.
Pegula will be motivated to finish it off after playing really strong tennis all week. Swiatek has a double motivation: the trophy and the ranking.
She spoke about her desire to return to number one after losing it, and this is a perfect chance for it. If she wins, she's number one, if she doesn't, she's not. That pressure didn't bother her against Sabalenka, so let's see what happens later today.