The Citizens bagged the double after their impressive form during the PSL bio-bubble, which saw them climb from 12th position to seventh on the final log standings.
Riekerink led his charges to five wins in seven games, claiming the scalps of the Mamelodi Sundowns, Orlando Pirates and SuperSport United along the way.
Erasmus pipped the likes of Sundowns star Themba Zwane, teammate Surprise Ralani and ex-Bidvest Wits goalkeeper Ricardo Goss to the gong.
The former Orlando Pirates forward netted four times in seven outings, playing an instrumental role in the Cape-based outfit clinching a top eight spot.
Meanwhile, Zwane managed two goals and three assists, with Ralani having netted twice. Goss conceded just five goals in nine games and kept four clean sheets.
Maritzburg United attacker Thabiso Kutumela also walked away with the Absa Goal of the Month award for his strike in their 2-2 draw with The Brazilians.