Victor Letsoalo gave the hosts the lead from the penalty spot in the 30th minute before Lesego Mangany sealed the contest in the 55th minute.
Marumo Gallants, who remain 11th on the table, fell to their second consecutive defeat after previously going eight matches unbeaten.
Royal AM, who gave owner Shauwn Mkhize the perfect birthday present, took another step towards CAF football next season.
Royal AM will next be in Nedbank Cup action
The KwaZulu-Natal will next be in action in a Nedbank Cup quarter-final clash at home against the University of Pretoria on Sunday, 10 April at 15:00.
Their next league match is away against Cape Town City FC on Saturday, 16 April at 17:00.