Sydney - Petra Kvitova sent defending champion Angelique Kerber packing from the rain-affected Sydney International on Thursday to book a semi-final spot and get an edge over her rival heading into the Australian Open next week.
It was always going to be a tight match with the pair tied 6-6 in 12 previous meetings.
Play was suspended early in the first set due to rain. They returned several hours later but the drizzle soon began falling again and it was back to the locker room for the two tournament drawcards.
They eventually resumed at 10:30pm and Czech fifth seed Kvitova, who won the title in 2015, took charge, quickly racing through the first set to put the German world number two on the back foot.
Kvitova kept the pressure on and got a crucial break in game four of the second set and there was no way back for Kerber who meekly surrendered 6-4, 6-1.
"The weather has not been great and it's not easy to wait in the locker room, but I was glad I could come back out and play so well," Kvitova said after reaching the semi-finals in Sydney for a fourth time.
Her reward is a clash with Belarusian qualifier Aliaksandra Sasnovich, who beat Switzerland's Timea Bacsinszky - on the comeback trail after a 14-month winless spell - 6-3, 6-3.
Australia's Ashleigh Barty followed up her giant-killing wins over world No 1 Simona Halep and former French Open champion Jelena Ostapenko by easily accounting for 10th seeded Belgian Elise Mertens 6-3, 6-3.
The 22-year-old is now on a six-match win streak, dating back to her career's biggest title at the WTA Elite Trophy in Zhuhai.
"Nice and solid today, I was pretty happy at the way I was able to come out and play," said Barty, ranked 15 in the world.
She will play seventh seed Kiki Bertens who blasted past Yulia Putintseva 6-2, 6-2 for a place in the final.
In the men's draw, veteran Andreas Seppi derailed top seed Stefanos Tsitsipas' title hopes.
Seppi, 14 years older than his 20-year-old Greek opponent, has only won three ATP titles in his career, but called on all his experience as he battled back for a gutsy 4-6, 6-4, 6-4 win.
"For some reason I always play my best tennis in Australia, so I really enjoy being here," said Seppi, who broke immediately in the second set after losing the first.
"It was very important to start well in the second set. Good to have an early break so I could play a bit more aggressive and it worked out in the end."
Australia has been a home away from home for the Italian in recent years.
In a trio of round-of-16 appearances at the Australian Open, he pulled off upsets against Marin Cilic in 2013, Roger Federer in 2015 and Nick Kyrgios in 2017.
Defeat was a blow for world No 15 Tsitsipas' preparations for the opening Grand Slam of the year in Melbourne next week.
He was one of the sport's most improved players last year, climbing from 91 after reaching finals in Barcelona and Toronto, losing both to Rafael Nadal, and was angling for the perfect start ahead of the Australian Open.
Seppi will now play third seeded Argentine Diego Schwartzman, who needed to fight hard to beat Japanese qualifier Yoshihito Nishioka 6-1, 3-6, 7-6 (7/1)
In other quarter-final action, fifth seeded teenager Alex De Minaur continued his strong start to the season with a 7-6 (7/4), 6-3 victory over fellow Australian Jordan Thompson.