World No 1 Aryna Sabalenka was defeated by 20-year-old Czech player Sara Bejlek at the Cincinnati Open on Wednesday. Sabalenka lost 7-6 (7), 6-4 to Bejlek.
During the first set tie-break, Sabalenka slammed her racket to the ground, causing its vibration dampener to detach. Play was paused while she searched for it before retrieving a new one.
Sabalenka's recent form has seen her reach one semi-final and no finals in her last seven tournaments since April. Her fourth-round loss in Cincinnati means Elena Rybakina has closed the gap to her No 1 ranking to 434 points.
Sabalenka will defend 2,000 points at the US Open as the defending champion, while Rybakina reached the fourth round last year. Rybakina, a finalist last week in Toronto, is reportedly playing well.