Kristyna Pliskova pulled off the biggest victory 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(7) defeat at the Birmingham grass court event on Wednesday.
The World No 112 fired down 24 aces as she beat world number three Karolina in their first meeting in a WTA event to stay on course for a second career title.
It was Kristyna's first win over a top-five ranked player and she will go on to play fellow Czech Barbora Strycova in the quarter-finals.
"I'm happy with the way I served today. I think we played the best that we could but it was not easy for us. She was nervous as well. The serve was the key and I'm happy I won," Kristyna said.
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.
"I know it's been six years since we last played," Kristyna, who beat her sister in the Eastbourne qualifiers in 2013, said.
"But we were both stressed about it and on centre court you never know how it's going to be. We played okay tennis, but it's like this, one had to win.
"I can imagine how she feels, I would feel the same. Maybe she feels worse because she was the favourite."
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.
"We had a deal before the match that whoever wins is buying something for the other one, so I get a present," Kristyna said.
"I think we do room service today and we just stay together because we shared a room. She has a day off, so maybe we'll go shopping again and she pays."
Nadal to prepare for Wimbledon at Hurlingham event
World No 2 Rafael Nadal has entered next week's Aspall Tennis Classic in Hurlingham to get some grass court play under his belt ahead of next month's Wimbledon Championships.
The tournament organisers confirmed Nadal, who has opted to skip competitive tennis since his 12th French Open title triumph earlier this month, will participate in two exhibition matches next Wednesday and Friday.
"I am always happy to play at The Hurlingham Club and be close to UK tennis fans," the 33-year-old Spaniard said in a statement.
"It is a prestigious ground in one of the best settings in the UK, making it the perfect way to warm up for Wimbledon."
The tournament will also feature last year's Wimbledon runner-up Kevin Anderson, Nick Kyrgios, Marin Cilic, Lucas Pouille, Felix Auger-Aliassime and Marcos Baghdatis.
Nadal, a 18-times Grand Slam winner, will be bidding for his third title at Wimbledon, which kicks off on July 1, after winning the tournament in 2008 and 2010.
He reached the semi-finals last year where he was beaten by rival Novak Djokovic in a five-set thriller.
Del Potro beats Shapovalov on another rain-hit day at Queen's Club
Juan Martin del Potro powered past Canadian Denis Shapovalov 7-5, 6-4 and into the second round of the Queen's Club Championships on Wednesday as spells of rain again caused headaches for the tournament organisers.
The Argentine sent down 11 aces and needed only two breaks of serve to beat world number 25 Shapovalov on Centre Court but hurt his right knee after slipping near the net in the second set and finished the match with pain and swelling.
Del Potro, who fractured his right kneecap last October, was scheduled to undergo tests on Wednesday.
He is set to meet Feliciano Lopez in the next round after the Spanish veteran rallied from a set down to beat Hungary's Marton Fucsovics 6-7(4), 6-3, 6-4.
Frenchman Jeremy Chardy beat Mikhail Kukushkin 6-1, 6-3 before rain brought matches on all courts to a temporary halt.
Rain caused the cancellation of a full day's play on Tuesday for the first time since the opening day of the 2012 tournament.
After action resumed a little before 1700 GMT, Swiss Stan Wawrinka sealed a comfortable 6-3, 6-4 victory over local hope Dan Evans while qualifier Aljaz Bedene got past Alex de Minaur 3-6, 6-4, 6-4.
However, rain stopped play again with Stefanos Tsitsipas leading Briton Kyle Edmund 6-3, 3-3 as the organisers pushed matches back to Thursday where action will begin at 1000 GMT.
Barty makes smooth transition to grass
French Open champion Ashleigh Barty made a smooth transition from Parisian clay to British lawns as the Australian opened her grasscourt campaign with an impressive 6-3, 6-4 victory over Croatia's Donna Vekic on Wednesday.
In her first match since winning her maiden Grand Slam title by beating Marketa Vondrousova at Roland Garros little more than a week ago, the 23-year-old began sluggishly but quickly found her rhythm to move through to the second round.
Vekic is no slouch on grass and Barty, emerging as one of the favourites for Wimbledon, said it was the "perfect test".
"I knew that I had to be sharp and I had to be ready. Otherwise it wouldn't even be a contest," world number two Barty said on court.
"It was nice and clean today out here. I was just really excited to come back out and kind of dust off the cobwebs a little bit."
Unseeded Jelena Ostapenko, who won the French Open two years ago but has struggled this year, ended the hopes of Britain's Johanna Konta, winning 6-3, 6-4.
Five-time Wimbledon champion Venus Williams also moved through with the 39-year-old defeating Aliaksandra Sasnovich.
Barty, a former junior Wimbledon champion, dropped serve early on but her deep, skidding sliced backhand began to work its magic as the Vekic errors mounted.
She broke twice to take the opening set and twice more to seize control in the second.
Vekic prolonged the contest to grab back one of the breaks when Barty served for the match. However, Barty made no mistake the second time around when she brought up match point with an ace and sealed victory when Vekic netted an attempted drop shot.
Barty's French Open title was somewhat unexpected seeing as she is not a renowned claycourter. Grass, on the other hand, is tailor-made for her game which is why all eyes will be on her at Wimbledon which starts a week on Monday.
The odds are against her following up her French title by winning Wimbledon. Only six women -- Margaret Court, Billie Jean King, Chris Evert, Martina Navratilova, Steffi Graf and Serena Williams -- have managed that in the professional era.
She will continue to hone her grasscourt skills against American Jennifer Brady who beat Lesia Tsurenko 6-3, 6-3.
