Aryna Sabalenka is becoming a target for rival Iga Swiatek at the WTA Finals in Mexico after losing her first group match of the week.

The current No. 1 is allowed no more defeats in the eight-woman field if she wants to hold off the season-long threat from Poland,

Sabalenka suffered a surprise setback as she lost 6-4, 6-3 to world No. 5 Jessica Pegula, with the victory enough to hand the American a group win and a semi-final spot at the year-ender.

Sabalenka’s 1-1 record hands swiatek an opportunity for a 2-0 mark if she beats Coco Gauff Wednesday evening in Cancun.

Sabalenka went down to defeat with 33 unforced errors and was forced to save nine of 14 break points off the Pegula racquet.

Sabalenka trailed 4-0 in the second set after dropping the first and was never able to close the gap despite saving six match points in the closing stages.

Pegula fought off a niggle, missing her two match points – the second on a double-fault – at 5-3 before struggling to close out victory in 89 minutes..

“I guess she just played great tennis,” Sabalenka said. “Yes, I could come back in this match — but it was too much.

“But, I still get a chance to pass the group, so I’m trying to stay strong.”