Sure enough, Australia's No.53 found the Italian world No.2 too tough to handle in Doha on Wednesday as he succumbed 6-3 7-5 in their last-16 clash.
After four-straight defeats to start his 2026 campaign, including a first-round exit at the Australian Open, Popyrin may have hoped things were looking up at last on Monday when he defeated Qatari wildcard in the last-32 for his first win in 2026.
But outclassing the world No.1159 was hardly the ideal preparation to face Sinner with the Italian looking sharp in his first tournament since losing to Carlos Alcaraz in the Australian Open final.
Popyrin, who'd reached as high as No.19 in the world just six months ago, just couldn't dent Sinner's high-quality serving, with the four-time grand slam champ dropping only three points on his delivery in the opening set.
Digging deep but still unable to conjure up a single break point opportunity, there felt an inevitability when Popyrin finally lost his serve for a second time at 5-5 in the second stanza, with Sinner then serving out for victory confidently after an hour and 24 minutes.
Remarkably, it was Sinner's 50th-straight victory over opponents ranked outside the top 50, a testament to his ruthless focus.
"I respect every player, but I always try to play my best tennis," Sinner said afterwards.
"The ranking, at the end of the day, is just a number. Everyone is playing high quality.
"Especially when the opponents don't have much to lose, you always have to stay very focused."
With Alcaraz beating French world No.60 Valentin Royer 6-2 7-5, the "big two" are again on collision course for a meeting in the final.
In the quarter-finals, Sinner will face rising Czech Jakub Mensik, the No.6 seed, while top seed Alcaraz will tackle Russia's seventh seeded Karen Khachanov.
The other quarters will feature a rejuvenated Stefanos Tsitsipas against No.5 seed Andrey Rublev, while eighth seed, Czech Jiri Lehecka, will face Frenchman Arthur Fils.
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