The Polish world No. 2, who was aiming for her third title in Stuttgart, lost 3-6, 6-3, 2-6 to the 24th-ranked Ostapenko in their women's singles clash.
It was the sixth meeting between the two players and the sixth victory for Ostapenko, public broadcaster Polish Radio’s IAR news agency reported.
Earlier this year, Ostapenko defeated Świątek 6-3, 6-1 in the semifinals of the Qatar Open in Doha.
Świątek in October parted ways with her Polish coach Tomasz Wiktorowski and hired Belgium's Wim Fissette to replace him.
She reached the semifinals in Stuttgart last year and won the clay-court tournament—sponsored by automaker Porsche—in 2022 and 2023.
(gs)
Source: IAR, PAP