World number one Aryna Sabalenka's preparations for her US Open title defence have suffered a setback when she lost to Sara Bejlek at the Cincinnati Open on Wednesday, while Tommy Paul saved a match point to knock out top seed Alexander Zverev.
Czech Bejlek claimed the biggest win of her career with a 7-6(7) 6-4 victory over Sabalenka in the round of 16, rallying from 5-1 down in a first-set tiebreak and 4-1 behind in the second set to secure her first win over a top-10 opponent.
The 20-year-old wrapped up the contest in about two hours and will next face Madison Keys in the quarter-finals.
Sabalenka's defeat means Elena Rybakina can replace her as world number one by reaching the Cincinnati final.
In the men's draw, American Paul battled back for a 4-6 7-6(6) 6-4 win over German world number three Zverev to reach the last eight in Cincinnati for the first time.
Zverev took the first set and trailed 3-4 in the second before the match was suspended due to rain.
Paul emerged from the nearly 90-minute delay looking the sharper player, saving a match point before levelling the contest as Zverev struggled to find his rhythm.
The German took a 4-2 lead in the third set but Paul dug his heels in to take control of the match, rallying to win four straight games in a stunning comeback.
Zverev's 14 aces were accompanied by nine double faults, with his service game looking shaky at times after he was called for a foot fault in the third set.
Paul will next play Flavio Cobolli after the Italian earlier defeated Spain's Rafael Jodar 4-6 7-6(3) 6-3.
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