Teenage Australian wildcard Alex De Minaur stunned Milos Raonic to reach the quarter-finals of the Brisbane International on Wednesday.

The 18-year-old is ranked 185 places below the Canadian at 209 in the world, but he broke the 2016 Wimbledon finalist three times and held to love in the last game of the second set to win 6-4 6-4 in front of a raucous crowd at Pat Rafter Arena.

De Minaur had benefited from the advice and support of Australia's Davis Cup captain Lleyton Hewitt prior to upsetting the fourth seed in Queensland.

"I honestly can't believe it," he said in an on-court interview.

"I'd like to thank everyone who came out and supported [me]. It's going to take a while for me to believe what happened just now. I'm lost for words actually. 

"At the end of the day, I was going to come out here and compete my hardest and I ended up playing an unbelievable match, it's crazy." 

De Minaur's opponent in the last eight will be American teenager Michael Mmoh, who overcame Mischa Zverev 6-2 5-7 6-4.

Earlier, Nick Kyrgios came from a set down to beat fellow Australian Matthew Ebden 6-7 (3-7) 7-6 (7-5) 6-2.

Both of the opening two sets stayed on serve until they were decided by tie-breaks, and it was Ebden who blinked first in the final set, world number 21 Kyrgios breaking his opponent twice to advance to the quarter-finals.

His next opponent is Alexandr Dolgopolov, the Ukrainian having brushed aside Horacio Zeballos in straight sets.