The Tanzania giants beat the reigning African champions 1-0 at the Benjamin Mkapa Stadium that brought an electrifying atmosphere with 30 000 fans in attendance.
Luís Miquissone's stunning strike put the home crowd into a state of euphoria as the 12th man helped Didier Gomes' side over the line to clinch a famous victory.
And Gomaa feels Mosimane is to blame for his first-ever defeat in the competition since joining the Red Devils and hopes it serves as a reality-check for the squad.
"Pitso Mosimane bears responsibility for his selections and his handling of the conditions of the game and the defeat to Simba," the six-time Champions League winner said on BeIn Sports, as per KingFut.
"He also made a mistake in the substitutions and cost Al Ahly the victory against Simba and lacked the offensive courage in the late substitutions."
Gomaa, who previously lauded the tactical organisation of Mosimane when he first arrived has warned there can't be any more slip-ups after AS Vita beat Al-Merrikh while Simba soared to the summit with six points.
"There is one positive about Al Ahly's defeat against Simba, which is the return of the players and Mosimane to their senses after a period of feeling the euphoria of achieving third place in the Club World Cup," Gomaa explained.
"Mosimane must prepare Al Ahly players in the best way for the next game against AS Vita Club because competition in the group has become more difficult after Al-Merrikh lost at home."
The Club of the Century face El Gaish in the league on Sunday at Al-Salam Stadium before hosting Florent Ibenge's Vita Club on Saturday 6 March.