Following each other on to the No.2 court at Monaco's Country Club on Thursday, Popyrin first saved two match points en route to outstaying world No.7 Caper Ruud 6-4 3-6 7-5 before de Minaur raised eyebrows through the ease with which he demolished old foe Daniil Medvedev 6-2 6-2.
It set up the rare treat for Australian tennis of having two players in the quarter-finals of a clay-court Masters 1000 event, with the tantalising prospect of further progress for the Sydneysider pals with 'Demon' facing Grigor Dimitrov and Popyrin up against Alejandro Davidovich Fokina in Friday's last-eight ties.
After a horror start to his season, Popyrin feels like he's starting his tennis year all over again as he earned his best victory of 2025 over Ruud.
A year after he knocked out the then world No.6 Andrey Rublev at Monaco's prestigious Country Club, the beanpole Australian this time accounted for another big name at his most successful European clay-court venue in a draining, near three-hour tussle.
Twice, Popyrin was a point away from bowing out when 5-3 down in the deciding set before he rallied and went on the attack against Norway's three-time grand slam finalist, reeling off the final four games for one of the best clay-court triumphs of his career.
It also put a dreadful start to his year behind Popyrin, who had only won two matches before turning up in the Principality for his first outing of the clay-court season.
"No, I'm 3 and 0 this year -- I'm forgetting about the start of the year for me!" laughed the 25-year-old, when asked about his dismal opening to 2025 after such an impressive breakthrough campaign last season.
"It was a tough start of the year but this week is a new week, and the year is really, really long, and I just have to put in the work and forget about the last couple of months -- and that's what I've done this week."
The two-hour 56-minute win over Ruud, sealed by a cross-court volley which was his 49th winner of the match, set up a clash with Davidovich Fokina, who also pulled off a shock by defeating British fifth seed Jack Draper 6-3 6-7 (6-8) 6-4.
Eighth seed De Minaur smiled he was now really finding his feet on clay after trouncing an out-of-sorts world No.11 Medvedev by earning seven breaks of serve in a one-sided affair lasting only 72 minutes.
Reckoning he'd taken confidence from how he had beaten Russia's former US Open champ at Roland Garros last year, world No.10 de Minaur feels he can be "dangerous" on the surface now as he reached the quarters in Monte Carlo for the second-straight year.
"I thought I executed really well, just had a slight lapse in concentration. But apart from that, I thought I was very smart and tactically played the right way," said de Minaur, who'll play 15th seed Dimitrov, a 6-3 3-6 6-2 victor over Novak Djokovic's Chilean conqueror Alejandro Tabilo.
Carlos Alcaraz, the second seed, beat German qualifier Daniel Altmaier 6-3 6-1 and will face rising French star Arthur Fils, while de Minaur's old nemesis Stefanos Tsitsipas looked in ominously good form with his 6-1 6-1 win over Nuno Borges.
The Greek sixth seed will play Lorenzo Musetti, who won the all-Italian showdown with Matteo Berrettini 6-3 6-3, in the last-eight.
