The victory put the Reds back above the ACT Brumbies in the standings and condemned the hapless Waratahs to a fifth successive defeat.
The Reds ran in seven tries to register their biggest win in Sydney - and their first in the city for eight years - while the injury-hampered Waratahs have now conceded 201 points as their horror season continues, heightening concern over the impact on Australian rugby's heartland.
Tate McDermott, Lukhan Salakaia-Loto and Filipo Daugunu all went over in the first half to take the Reds to a 22-9 lead at the interval.
Any hopes of a home comeback after half-time were quickly smothered by a try from Reds prop Taniela Tupou although the Waratahs quickly responded with a try of their own when Lalakai Foketi's goose stepping evaded the Reds' defence and allowed Will Harris to dive off.
Hooker Mafi, who had come on at half-time, then scored two tries in the space of five minutes, both from rolling mauls, as the difference in forward strength between the two line-ups was cruelly exposed.
He completed his hattrick as he charged over from some five metres out with three minutes left to take his try tally for the season to six.