Elena Rybakina's Wimbledon title defence preparations suffered a setback when she was beaten in the second round at the German Open.
The second seed, 24, lost 6-7 (1-7) 6-3 6-4 to Croat Donna Vekic in Berlin.
The Kazakh world number three had beaten Russian Polina Kudermetova the previous night, with matches delayed because of rain.
Rybakina was one of seven of the world's top-10 ranked women competing at the Wimbledon warm-up event.
Vekic faced just two break points against the Kazakh, who pulled out of the French Open before her third-round match earlier this month because of illness.
The Australian Open quarter-finalist saved them both and went on to end Rybakina's eight-match winning streak on grass.
Rybakina's Wimbledon final opponent Ons Jabeur also began her grass-court season with defeat in Germany on Tuesday.
Elsewhere, French third seed Caroline Garcia secured her place in the quarter-finals with a 6-3 6-2 win over Australian qualifier Jaimee Fourlis.
Maria Sakkari, who reached the semi-finals of the US and French Opens in 2021, beat Alize Cornet 6-4 6-2, having fallen short against the Frenchwoman in Nottingham last week.
Czech Marketa Vondrousova, Roland Garros runner-up in 2019, beat Canadian 2019 US Open champion Bianca Andreescu 7-6 (7-0) 7-5 in one of several first-round matches that was postponed to Wednesday because of the rain.
Having reached the semi-finals of the Libema Open in the Netherlands last week, Belarusian Aliaksandra Sasnovich continued her strong grass-court form with a 6-4 6-4 victory over two-time Grand Slam champion and compatriot Victoria Azarenka.
Former world number one Azarenka also suffered a shock defeat last week by American teenager Ashlyn Krueger at the Libema Open