(Reuters) -World number one Aryna Sabalenka secured a semi-final berth at the WTA Finals by beating Italian fourth seed Jasmine Paolini 6-3 7-5 on Monday to stay unbeaten in the purple round-robin group.

The 26-year-old is on the brink of clinching the year-end number one ranking. A win over Elena Rybakina in the final group match on Wednesday or a loss from her rival, Poland’s Iga Swiatek, would seal the year-end top spot for the Belarusian.

Sabalenka’s win combined with Chinese Zheng Qinwen’s earlier 7-6(4) 3-6 6-1 victory over Rybakina ensured the top seed will finish first in her group regardless of her final result on Wednesday, making her the first player to reach the final four.

Australian Open and U.S. Open champion Sabalenka also won her opening match in Riyadh against seventh seed Zheng. The Chinese player and Paolini, with 1-1 records, both remain in contention for the semis and meet on Wednesday.

Swiatek is the only player who can overtake Sabalenka. The 23-year-old, who plays Coco Gauff on Tuesday, needs to retain her title undefeated and hope Sabalenka loses her remaining matches in order to claim the year-end number one spot.

“I’m proud of myself. Not only myself, my team,” Sabalenka said after her win. “We were able to overcome a lot of things. To be able to show such great tennis and become world number one, It’s teamwork. It’s not only me.”

“Nobody sees the behind the scenes work. 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.”

Sabalenka is the first player to reach back-to-back semis at the WTA Finals as world number one since Serena Williams in 2013-2014.

Zheng, 22, notched her first career win over 25-year-old Kazakh Rybakina in their third meeting, bouncing back from her loss to Sabalenka to become the second Chinese player after Li Na to win a match at the Finals since they started in 1972.

Rybakina suffered her second defeat, having arrived in Riyadh with fitness issues. Zheng, by contrast, came into the event after winning titles in Palermo and Tokyo plus Olympic gold in Paris.

“I’m really happy to win this match because I’d never beaten her before and she’s one of the greatest players right now on tour,” Zheng said.

“Even though I had a chance in the second set and didn’t take it, I’m happy I came back in the third set and stayed focused.”

(Reporting by Shifa Jahan in Bengaluru; Editing by Christian Radnedge and Ken Ferris)