Aryna Sabalenka became the first player to book her place in the WTA Finals semi-finals after her straight-sets win over Jasmine Paolini on Monday.
The Belarusian had to dig deep in the second set but prevailed in 91 minutes, beating the Italian 6-3 7-5 in Riyadh to secure top spot in the Purple Group after two games.
While Sabalenka cruised through the first set, she was almost forced to a decider, but saved two set points in the 10th game of the second to level the score at 5-5 before going on to claim the victory.
In doing so, she became the first player to reach back-to-back semi-finals at the tournament as world number one since Serena Williams in 2013-14.
Having won three of her previous four tournaments and won 22 of her 23 matches in that time, Sabalenka is now just one win away from securing the year-end world number one spot for the first time, a feat she can achieve if she beats Elena Rybakina on Wednesday in the final round-robin match.
And she can go into it with confidence after improving her record against top-five opponents in 2024, with this her fifth such triumph.
"I'm proud of myself. Not only myself, my team," Sabalenka said.
"We were able to overcome a lot of things. To be able to show such great tennis and become World No. 1. It's teamwork. It's not only me. The behind-the-scenes work nobody sees.
"But they do a lot for me. I really appreciate them for everything they do for me. This is motivation for me to keep winning on this court. Those guys deserve to be called the best team ever."
In Monday's other match, Zheng Qinwen kept her hopes of reaching the final four alive with her win over Rybakina.
The Olympic champion was forced to go the distance though, despite getting the first break in the first and second sets, but eventually came out on top 7-6 (7-4) 3-6 6-1 in just under two-and-a-half hours.
Since the event's inauguration in 1972, Zheng is just the second Chinese player to win a match at the WTA Finals after Li Na.
It was a milestone victory for the 22-year-old as well as she earned her 50th win of 2024, improving her record to 50-17, making her the first Chinese player in the Open Era to hit that mark in a calendar year, though she acknowledged she could have made things easier for herself.
"I was the one to make the first break, and then I let her back in the first," Zheng said.
"Then it happened again in the second. But in the third set, I talked to myself. I broke her first and I stayed focused.
"Finally, in the third set, I start to play my tennis again. So, I'm really happy to win the match."