World number two Iga Swiatek overcame a shaky start to defeat Wimbledon champion Marketa Vondrousova in straight sets in her opening WTA Finals match in Cancun.
In Monday's other clash, US Open champion Coco Gauff opened her tournament with a 6-0, 6-1 drubbing of Tunisia's Ons Jabeur.
Polish star Swiatek looked out of sorts in an error-strewn first set in which she trailed 2-5 before roaring back to clinch a 7-6 (7/3), 6-0 victory.
The 22-year-old four-time Grand Slam champion is bidding to reclaim her world number one ranking from Aryna Sabalenka at this week's season-ending finals in Mexico.
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