According to the differences in ratings, you would have lost anyway
Your players played the entire game cause your coach figured it was a better option (according to their stats and stamina) than to substitute them with your bench players (which probably was), so it's not a bug, it's the way it's supposed to work.
For an example, imagine you have michael jordan playin sg in your team, and your cousin who plays basketball in the local team as his backup. I figure the coach would let Jordan play the full game if it's one with a tough opposition as changing him for your cousin, even if jordan is very tired in the end of the game, wouldn't make your cousin better
Anyway, the guy playing agains't you has WAY better player than you, and he would have won anyway, maybe by more