She made a dreadful start by dropping serve in the opening
game. The second seed was broken twice more as 2019 French Open runner-up
Vondrousova raced away with the first set.
Osaka broke in the second set but relinquished the early
advantage with a double fault that allowed Vondrousova to level at two games
apiece.
The four-time Grand Slam winner grappled with inconsistency,
and even when given a sniff of regaining the initiative she had no response to
Vondrousova's array of crafty drop shots.
Osaka saved two match points as she served to stay alive at
4-5 but Vondrousova converted at the third time of asking as the Japanese star
smacked a backhand wide.
Vondrousova, ranked 42nd, will go on to face Spain's Paula
Badosa or Nadia Podoroska of Argentina.