Sabalenka lost in straight sets, 4–6, 3–6, to 34th-ranked Czech Nikola Bartunkova.
"She is a legend. So I am very happy that I won the match," Bartunkova said.
Sabalenka never got her game under control and in the fourth game of the second set, the visibly frustrated Belarusian threw her racket after losing a point.
The Belarusian’s exit means the second seed in the tournament is out. On Saturday, world number one Yelena Rybakina surprisingly lost to 118th-ranked Armenian Alina Charaeva.
