Sloane Stephens was sent crashing out of the first round of the Tokyo Open by Donna Vekic, but Victoria Azarenka overcame Kurumi Nara on Tuesday.
Fifth seed Stephens slipped to a 6-4 6-4 defeat to Vekic in under an hour and a half in the Japanese capital in a match that saw both players struggle to hold serve in the second set.
It marks Vekic's second victory over Stephens this year following her triumph at Wimbledon.
"I felt good. I beat her last time we played, so I knew my game plan and I tried to stick to it," she said.
"I'm playing really well this year. I'm improving a lot. Even when I lose, I keep working hard and doing the right things, and I feel like it's showing on the court."
Next up is a meeting with Johanna Konta, who hammered Gabriela Dabrowski 6-2 6-0.
Former world number one Azarenka, handed a wildcard for the tournament, withstood a tough challenge from home favourite Nara to earn a 6-4 7-5 triumph.
The Belarusian mixed 25 winners with 41 unforced errors in her first outing since losing to Stephens at the US Open.
Ashleigh Barty (7) and Barbora Strycova (8) both reached round two, the former needing three sets to beat Coco Vandeweghe, while the latter defeated Zarina Diyas 6-4 6-4.
Rounding out the action, Alison Riske was a 6-4 6-4 winner against Eugenie Bouchard.
