At the ATP 250 Vienna Open indoor hardcourt event, de Minaur put paid to the hopes of local Filip Misolic, on Wednesday evening, just two days after knocking out another Austrian, Jurij Rodionov, to notch up his 300th tour-level win.
Setting off on what he smiled would be his next 300, the Australian No.1 this time turned out to be a notch above his counterpart Misolic, the world No.95, who was cheered to the rafters by the crowd at the Wiener Stadthalle but still succumbed 6-4 6-4 in just under an hour-and-a-half.
He wasn't quite at his sharpest, seeming a bit frustrated at some of the chances he spurned, but it was another professional job from the 'Demon' as he chalked up his 52nd win of 2025.
World No.7 de Minaur, moving ever closer to a place in the end-of-season ATP Finals in Turin, took a grip from the outset, earning a break at the fourth attempt in a lengthy opening game.
Far from overawed, wildcard Misolic kept de Minaur honest, but couldn't exert any real pressure on the Australian's delivery as he lost the first stanza in 43 minutes.
The Austrian then served up an error-riddled game to go 2-1 down in the second and was again forced to play catch-up. The Sydneysider did offer up his only three break point opportunities when leading 3-2, but once he'd repelled those, he eased to his 11th quarter-final of the year.
Earlier, Popyrin, who's slipped from 19 to No.48 in the world over the past couple of months after surrendering his treasure trove of ranking points from his 2024 Canadian Open triumph, was beaten 7-6 (7-5) 6-3 by a rejuvenated Italian Matteo Berrettini in their round-of-32 match.
Even a dozen aces weren't enough for Popyrin, who had a chance, when 5-4 up in the opening-set tiebreak, to serve it out for a 7-4 win, only to lose the next three points instead.
Former Wimbledon finalist Berrettini could be de Minaur's last-eight opponent, but will first have to get past doughty Briton Cameron Norrie in the round of 16.
Top seed Jannik Sinner was in coruscating form, opening his bid by beating German Daniel Altmaier 6-0 6-2 in two minutes under an hour. His first set was so immaculate, he conceded just six points.
Daniil Medvedev was another notable winner. Fresh from his Almaty Open victory, his first tournament triumph in 882 days, the Russian sixth seed made hard work of downing Portugal's Nuno Borges 6-4 6-7 (7-9) 6-2.
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