The 27-year-old Windhoek-born forward netted after 10 minutes in Pretoria and further goals from Lebohang Maboe, Lesedi Kapinga and Andile Jali gave the hosts a four-goal lead just 28 minutes into the opening half.
Shalulile has scored 10 goals in domestic league and cup competitions this season, four less than frontrunner Bradley Grobler of SuperSport United.
He has also netted three times in the CAF Champions League and Sundowns need one win from three remaining group matches to clinch a quarter-final place.
Sundowns joint coach Manqoba Mngqithi has hailed the Namibian, who joined Sundowns last year after five years with another top-flight club, Highlands Park.
"Peter gives you 100 percent commitment and not only scores regularly, but creates goals for others. He is busy repaying the club president (Patrice Motsepe) for spending a lot of money to buy him."
Sundowns triumph sets up a blockbuster April 21 quarter-final against Orlando Pirates and the winners will be installed as favourites to pocket the seven million rand (390,000 euros) first prize.