McKenzie, who lost his first fight to Hiroaki Hiraoka of Japan at London 2012 last summer, won all four of his -60kg bouts for victory in Uruguay.
The 23-year-old began with a win over home hope Rodrigo Gamou by ippon before victories by the same method over Youssef Youssef and Japan's Yusuke Shibata.
He met Eric Takabatake of Brazil in the final and brushed him aside for gold while Ben Fletcher and Matthew Clempner followed suit in the -100kg and +100kg respectively.
Nathon Burns reached the -66kg final but couldn't see off a Brazilian opponent like training partner McKenzie as Charles Chibana ensured he had to settle for silver.
That still represents Burns' career-best result while Andy Burns, Lewis Keeble, Graham Trinder and Connie Ramsay all finished fifth while Gregg Varey was seventh.
- Sports & Recreation