Iga Swiatek was dumped out of the Toray Pan Pacific Open in the quarter-finals by Russian Veronika Kudermetova.
After being bundled out of the US Open, Iga Swiatek has already come to terms with no longer being world number one when the tournament ends.
Iga Swiatek's reign as world number one and US Open champion was brought to an end by a spirited Jelena Ostapenko at Flushing Meadows on Sunday.
Top seed Iga Swiatek made short work of her friend Kaja Juvan on Louis Armstrong Court at the US Open on Friday.
Carlos Alcaraz and Iga Swiatek, the current world number ones, will bid to defend their US Open titles they won last year, but a host of rivals will be out to dethrone them.
Coco Gauff scrapped her way to a maiden win over world number one Iga Swiatek to reach her first WTA 1000 final at the Southern and Western Open in Cincinnati.