Aryna Sabalenka and Coco Gauff were both dumped out of the WTA tournament in Berlin in the second round.
After Wimbledon champion Elena Rybakina was beaten on Wednesday, Sabalenka and Gauff both followed on Thursday.
Gauff won only four games against Russian Ekaterina Alexandrova, who is bang in form on the grass having won the Libema Open in the Netherlands last week, going down 6-4 6-0.
“Grass is not my favourite surface, but somehow I’m managing to play so well on it. And maybe the score looks easy, but it’s never like that because she played amazing,” said Alexandrova, who won her seventh straight match.
“I needed to stay focused during every single point to keep it that way. I’m just hoping I can keep this form as long as I can.”
The player Alexandrova beat last week, fellow Russian Veronika Kudermetova, continued her good form by knocking out top seed Sabalenka 6-2 7-6 (7-2).
Both Sabalenka and Gauff were playing their first tournament on grass – and their first since the French Open.
“For me it’s very important to play like that today,” Kudermetova said. “I always believe in myself. I know I can play really well, and I always believe.”
Last year’s Wimbledon quarter-finalist Jule Niemeier faces an anxious wait after being forced to retire from her match with Marketa Vondrousova trailing 6-3 6-5 after falling and hurting her right wrist.