Two years after upstaging the great Novak Djokovic in a seismic US Open triumph, Popyrin has slumped to No.139 in the world as he battles a crisis of confidence.
But after toiling through qualifying just to make the main draw, Popyrin toiled for another two hours 12 minutes to see off Argentine Roman Andres Burruchaga 4-6 7-5 6-3 to notch his first ATP-level win since May.
The breakthrough was only Popyrin's ninth win of a lean 2026 campaign and vaulted to the one-time world No.19 into a second-round contest with US seventh seed Taylor Fritz or another Argentine, Thiago Agustin Tirante.
De Minaur, meanwhile, looked to be cruising before fellow Sydneysider James Duckworth put the world No.7 through the ringer late on.
Runner-up in 2023, de Minaur was a set and 3-1 up before Duckworth fought back hard seeking a first win over his countryman in three meetings.
But de Minaur held firm to fend off six set points and progress 6-2 7-6 (8-6) and book a third-round date with either Brit Cameron Norrie or Peru's Ignacio Buse.
"In the first set everything was flowing," de Minaur said after the one-hour, 46-minute dogfight.
"I was up a break, had a couple more chances to go up by a double break and all of a sudden it slips away.
"Then all of a sudden momentum shifts and we got into a battle. So I am glad I was able to sneak through. There are a couple of things I need to tighten up on, but we live to fight another day."
While de Minuar and Poprin move on, fellow Australian Adam Walton crashed out with a 6-3 6-4 loss to American Jenson Brooksby.
In the women's WTA event in Toronto, Tahlia Gibson continued her stellar 2026 season with an upset 7-5 6-1 second-round win over Polish 18th seed Maja Chwalinska.
Gibson's 28th win of a breakout year earned her a crack at Russian 16th seed Ekaterina Alexandrova.
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