Rodgers was left bemused by a below-par effort from a mixed Liverpool side in the 3-2 fourth-round defeat at Boundary Park as they were hardly in the game in the first half.
Things improved a little when he brought on added experience in the second period, but Joe Allen's 80th minute goal came too late to turn around a Sunday afternoon the red-faced Liverpool manager would rather forget.
"We are bitterly disappointed. We started the first half poorly and we started the second half and got punished," Rodgers said. "We've got a big week of games but our mentality in that opening period was poor and it ended up costing us.
"I was disappointed with the young players today I've got to be honest.
"We are trying to give them experience and let them see what it was like to play for Liverpool. It is not just about playing for Liverpool, you have to be competitive and be part of a group that is going to challenge for trophies.
"I thought how we reacted to that and how we performed, knowing that is what we are looking for, was disappointing.
"It is not enough to play for Liverpool and get up for the Arsenal and Manchester City games (later this week) because if we are going to win trophies you need to be able to come to places like Oldham and win and we weren't good enough for that.
"We were just too much on the back foot early on, you really have to be aggressive. These are different games to the Premier League: Premier League games are nice, you go in and teams will pass the ball and give you time to get your shape.
"These games are a different type of football, you have to roll your sleeves up be strong and aggressive and unfortunately for us there were too many who weren't.
"It is just a different type of football where you have to stand up and be counted. It is great to put young players in but you have to have personality and the young players disappointed."