Kristyna Pliskova pulled off the biggest win of her career but it was bad news for twin sister Karolina who was on the receiving end of a 6-2 3-6 7-6 (9-7) defeat at the Birmingham Classic WTA event.
The world No.112 fired down 24 aces as she beat world No.3 Karolina in their first meeting in a WTA event.
It was her first win against a top-five ranked player and she will go on to play fellow Czech Barbora Strycova in the quarter-finals.
The twins set up the second-round clash after Karolina accepted a wildcard and defeated Mihaela Buzarnescu on Monday while Kristyna came through three rounds of qualifying before beating Viktoriya Tomova.
Kristyna, two minutes older than her sister, broke early in contest and raced ahead 5-1 before closing out the opening set with an ace.
Former US Open finalist Karolina, who lost the last clash between the pair at the Eastbourne qualifiers six years ago, responded strongly to drag the match into a decider.
Kristyna surged 4-1 ahead in the third set but Karolina fought back to force a tiebreak.
A third double fault by Karolina at 7-7 gave her twin match point and Kristyna held her nerve to seal a memorable victory.
Earlier in the day Australia’s Ashleigh Barty beat Donna Vukic 6-3 6-4 in her rain-delayed first round match.
Five-time Wimbledon champion Venus Williams overpowered Aliaksandra Sasnovich 6-3 6-4 and 2017 French Open winner Jelena Ostapenko beat British No.1 Johanna Konta.