Sundowns were made to fight back from behind to salvage a point at the Estadio 11 de Novembro on Saturday afternoon as they played to a 2-2 draw away to Petro.
The result saw The Brazilians' lead at the top of Group C cut to just two points after second-placed Wydad Casablanca beat USM Alger 3-1 at home on Friday evening.
Reflecting on his side's performance, Mosimane felt they lacked the necessary intensity to see out the desired result as he blamed the players' poor mentality.
"We tried to win but I don't know if we really tried hard to win hey. I didn't see my team try very hard to win this game, to be honest," said 'Jingles' after the match.
"But the mentality is that sometimes the players know they have already qualified, and they don't give the right intensity to the match, but it's okay.
"Mathematically, it's okay if you look at the group, but the prize is to finish at the top of the group. At this point, okay we are top but we're still not qualified as top of the group until matchday six happens.
"So, unfortunately we still have to play for a result in South Africa [against Wydad]. I thought we won't play for the result, but now we have to."
While USMA and Petro play a dead-rubber tie in Algers, all eyes will be on the battle for top spot in Group C when Downs host WAC at Lucas Moripe Stadium next Saturday at 15h00.