Birmingham (United Kingdom) (AFP) - World number three Karolina Pliskova lost to her twin sister Kristyna, while French Open champion Ashleigh Barty started her grass court season with a win at the Birmingham Classic on Wednesday.
In the first meeting of the Pliskova twins since 2012, it was 112-ranked Kristyna who edged a three-set thriller 6-2, 3-6, 7-6 (9/7).
Kristyna Pliskova will take on another Czech player next as she faces Barbora Strycova for a spot in the quarter-finals.
Barty suffered no such shocks as she saw off a bright start from Croatia's Donna Vekic in her first match since lifting a first Grand Slam title to win 6-3, 6-4.
"I think it was probably as smooth as it could have gone," said Barty, who set up a second round meeting with American Jennifer Brady.
"I felt really good with my feet on the grass. We haven't had a hell of a lot of grass court time because of the weather but in a sense that made it even better because it was fresh, it was new.
"I could really just play by feel and try and work my way into the match."
The Australian shot to number two in the world rankings by winning in Paris earlier this month and could even end the week as number one if she outperforms Naomi Osaka in England's Midlands.
However, Barty insists she is not yet feeling any strain of being a Grand Slam champion.
"I don't feel any different myself," she added. "I'm still the same Ash Barty that I was three weeks ago. I'm the same Ash Barty I was two years ago."
A former French Open winner herself, Ostapenko has struggled with injuries this season but has now posted back-to-back wins for just the second time this year.
Venus Williams progressed to round two as the 39-year-old eased past Aliaksandra Sasnovich 6-3, 6-4.