After a goalless first 45 minutes, Mbella gave Kotoko the lead with a penalty before netting twice in the space of six minutes to put the game to bed.
Midfielder Elijah Addai scored a consolation for the Miners in the 85th minute.
Kotoko thanks to the win are three points clear at the top of the league, while Ashgold are closer to the relegation zone as they sit 15th.
Title contenders King Faisal were stunned in Techiman as they fell to a 2-0 defeat against struggling Eleven Wonders at the Ohene Ameyaw Park.
Third-placed Aduana Stars secured a narrow 1-0 victory at Elmina Sharks to return to winning ways.
Bechem United beat Real Tamale United 2-0, Legon Cities shocked Dreams 1-0 in Dawu, and Great Olympics shared the spoils 1-1 with Karela United.
On Saturday, a solitary strike by James Sewornu ensured Hearts of Oak beat Bibiani Gold Stars to stay unbeaten in the league since November 2021.
Accra Lions and WAFA played out a goalless draw with the Academy Boys second from bottom, and Medeama were held 1-1 at home by Berekum Chelsea.
— Asante Kotoko SC (@AsanteKotoko_SC) January 9, 2022