It was Sinner who looked sharpest early, taking the first three games of the opening set before securing a double break, but while Auger-Aliassime struggled to deal with the Italian's serve early on, it was not the case as the match wore on.
Sinner won 80 per cent (12-of-15) of his first serve points in the first set, but that number dwindled down to 62 per cent in the second and 50 per cent in the third as Auger-Aliassime grew into the contest and stormed home late.
Auger-Aliassime will face the in-form Borna Coric in the quarter-finals after the Croatian backed up his shock upset win against Rafael Nadal by defeating 15th seed Roberto Bautista Agut 6-2 6-3.
Earlier in the day, fresh off his own upset win against Nick Kyrgios, American Taylor Fritz needed two and a half hours to get past Russia's Andrey Rublev 6-7 (4-7) 6-2 7-5.
Fritz will play world number one Daniil Medvedev for a spot in the semi-finals after the top-seeded Russian was made to work hard for his straight-sets 7-5 7-5 win against Canada's Denis Shapovalov.
World number four Carlos Alcaraz was incredibly impressive against the big-serving Marin Cilic, finding an extra gear in the second set to run away with a 7-6 (7-4) 6-1 victory.
It was similarly strong work from world number seven Stefanos Tsitsipas, creating 14 break point opportunities in his 6-3 6-3 handling of Argentina's Diego Schwartzman.
In an all-American showdown it was 37-year-old John Isner outlasting 22-year-old Sebastian Korda 7-6 (7-3) 1-6 7-6 (7-4) in yet another win for Isner without breaking his opponent's serve a single time.
The final match of the night was a quick one, as world number 11 Cameron Norrie needed just 59 minutes to defeat American qualifier Ben Shelton 6-0 6-2.