World number 208 De Minaur put his Canadian opponent under pressure early on in the contest, grabbing a break in the third game before hanging on to take the first set.
A rusty Raonic tried to mount a comeback late in the second set but De Minaur resisted the charge of the world number 24 and pushed on for the biggest win of his career.
Mmoh, 19, earlier saved six break points and converted four of his own to upset eighth seed Mischa Zverev 6-2 5-7 6-4 for only his second victory on the ATP Tour.
Nick Kyrgios overcame pain in his knee to beat Australian compatriot Matthew Ebden 6-7(3) 7-6(5) 6-2 in his first singles match since a hip injury ended his season in October.
Kyrgios, who took a medical timeout while trailing 4-5 in the opening set, received treatment again two games later and struggled to find his feet as Ebden edged the tiebreaker.
The world number 21 hit back in the second set and pulled away in the decider to set up a clash with Alexandr Dolgopolov who beat Argentina's Horacio Zeballos 6-1 6-2.
"It took me a while to get used to playing a match again," Kyrgios said after the 131-minute encounter.
"I've been training here for so long and training on centre court, it kind of didn't feel like a match. The longer the match went, the better I played, the looser I got. I knew it was going to be a tough day today. He's a tough competitor."
(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Christian Radnedge)
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