The Italian was the only seeded player to move out of the Round of 16 on Wednesday, and he did so in just 85 minutes.
Sinner, No. nine in the world, won 84 per cent (27 of 32) of the points on his first serve compared to 64 per cent for his opponent, didn't drop a game on serve in the match and won five games in a row to eliminate Bublik.
Croatia's Borna Coric, the third seed, lost to American Mackenzie McDonald 6-4, 6-4, and Emil Ruusuvuori of Finland, defeated seventh seed Ugo Humbert of France, 6-2, 6-7 (6), 6-4.
Rinky Hijikata of Australia ousted Marc-Andrea Huesler of Switzerland 2-6, 7-5, 6-3 in the day's only other action.
Boss Open
Fourth-seeded Hubert Hurkacz of Poland was pushed to the limits by Japan's Yosuke Watanuki but emerged a 4-6, 7-6 (5), 7-6 (5) winner in Stuttgart, Germany.
The entertaining two-hour, 21-minute match featured 48 aces, with 27 of them coming from Watanuki, fueling his 51 winners against 14 unforced errors. Still, Hurkacz was able to escape two tiebreaks to move to the quarterfinals.
There, he'll face Christopher O'Connell of Australia, who defeated Lorenzo Sonego 7-6 (5), 6-3. Sonego's fellow Italian, sixth-seeded Lorenzo Musetti, had no trouble against Gregoire Barrere of France in a 6-3, 6-3 win.
Musetti next faces third seed Frances Tiafoe, who saved all three break points in a 7-6 (2), 6-4 defeat of Jiri Lehecka of the Czech Republic.
