Iga Swiatek began her US Open title defence with an emphatic first-round victory as eighth seed Maria Sakkari fell to a surprising loss.
World number one Swiatek breezed to a 6-0 6-1 win over Sweden's Rebecca Peterson in 58 minutes.
Sakkari had a day to forget on Court 17 as she was knocked out by world number 71 Rebeka Masarova of Spain.
The Greek had been 4-1 up in the first set but Masarova responded in thrilling fashion to claim a 6-4 6-4 win.
Swiatek has won both previous meetings with world number 86 Peterson and came through this encounter on Arthur Ashe Stadium in imperious style.