Competing a couple of hundred kilometres from where his father Helmut claimed Olympic silver in Calgary in 1988, Mayer charged down the Lake Louise mountain to triumph by nearly half a second.
The 29-year-old Austrian skied flawlessly, hitting speeds of 120 kph to end his run of four second-place finishes on the mountain.
For his sixth World Cup career victory -- three in super-G and three in downhill -- Mayer beat Italian Dominik Paris by 0.40 seconds, while Austrian Vincent Kriechmayr and Swiss Mauro Caviezel tied for third, 0.49 seconds off the pace.
Paris, the lead singer in a heavy metal band, had to settle for runner-up for the second successive day after being pipped in the downhill on Saturday.
Mayer is a double Olympic gold medallist, winning super-G in Pyeongchang in 2018 and downhill in Sochi in 2014. (Reporting by Andrew Both in Cary, North Carolina; editing by Clare Fallon)