After a game the Citizens dominated for almost the entire 90 minutes, McCarthy's side left empty-handed as they failed to find a way past Usuthu.
"If you don't score they punish you, we created chances and dominated the game but we failed to win, the loss feels like a sucker punch." McCarthy said after the match.
"I always hear people saying football can kill you. For the first time I felt like that, we didn't deserve a loss but that's football for you."
The former Orlando Pirates striker gave credit to Cavin Johnson's side for snatching a win with a cracking free-kick by Tapelo Nyongo.
"We must give them credit for the win, they managed to walk away with a win in a tough situation as they were under pressure almost the whole game," he added.
McCarthy also felt his side lacked aggression in terms of punishing their opponents in front of goal.
"We need to be aggressive. I'm not talking about playing rough and kicking our opponents, I'm talking about goals, punish them, we should win such games," he explained.
On whether the loss had an impact on their league target for the season, McCarthy said their only focus is on improving as a team.
He added: "Yes, a win would've made an impact on the log but we are running our own race. During the week we work on how we can improve, then on game day we play and hope to do well."