Swiatek won her match on Thursday, but didn't qualify for the semis in Riyadh.
Without seven-time champion Novak Djokovic, the ATP Finals will have a different look this year.
Zheng has won 30 of 35 matches since Wimbledon.
Coco Gauff earned her second win in 14 tries over the defending WTA Finals champion.
For the first time in 23 years, no member of the Big 3 will participate in the ATP Finals.
Sabalenka can clinch year-end No.1 with a win on Wednesday.
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