Sydney - Andreas Seppi called on all his experience on Thursday to derail top seed Stefanos Tsitsipas' Sydney International title hopes and ease into the semi-finals, with Belarusian Aliaksandra Sasnovich the first woman to make the last four.
Veteran Seppi, 14 years older than his 20-year-old Greek opponent, has only won three ATP titles in his career but remained on course for another 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's reward is a clash with either third seeded Argentine Diego Schwartzman or Japanese qualifier Yoshihito Nishioka.
In other quarter-final action, fifth seeded Alex De Minaur takes on fellow Australian Jordan Thompson while France's fourth seed Gilles Simon faces another Australian, John Millman.
The first woman to book a semi spot was qualifier Sasnovich, who beat Switzerland's Timea Bacsinszky - on the comeback trail after a 14-month winless spell - 6-3, 6-3.
But she has a daunting task ahead, playing either world number two and defending champion Angelique Kerber or fifth seed and 2015 Sydney winner Petra Kvitova, who meet in a match headlining Thursday's night session.
In 12 meetings on tour, Kerber and Kvitova have won six each and split their two meetings in 2018.
In other women's quarters, seventh seed Kiki Bertens faces Yulia Putintseva while Ashleigh Barty - who beat world number one Simona Halep on Wednesday - is up against 10th seed Elise Mertens.
Diego Schwartzman (ARG x3) bt Yoshihito Nishioka (JPN) 6-1, 3-6, 7-6 (7/1)