The Hoops arrived at Signal Iduna Park in optimistic mood and in free-scoring form after 17 consecutive wins, including a 5-1 victory over Slovan Bratislava in their opening match of the Champions League.
But they were on the end of the kind of thrashing that they have been handing out themselves in recent weeks.
Daizen Maeda’s ninth-minute equaliser was the high point for the travelling support but Karim Adeyemi netted the first goal of his first-half hat-trick two minutes later.
Rodgers said: “It was a tough watch to be honest. We weren’t quite at our best and they showed why they’re a top, top team.
“We didn’t make the start that we wanted and then, like I said to the players afterwards, I don’t think I’ve been involved in a game where I felt that every single mistake that we made got punished.
“And that’s the level. Any misplaced pass or moment that they had, it just seemed to end up in the back of the net. And then on the other side, we had a couple of moments in the second half and it didn’t just quite fall for us.
“At this level, especially away from home against a top team, you need to be at your highest level. We weren’t and they were.”
Some basic errors on the ball were punished, including Maeda twice losing the ball to Adeyemi before the forward finished in lethal fashion.
“That’s the learning that comes away from this level,” Rodgers said.
“I think that we may have got spooked a little bit early on. We get the equaliser and very, very quickly we’re then 2-1 behind. They get a foothold in the game, start to move it well and we start to chase it a little bit.
“So it was a mixture of our positioning but also then just our quality and our passing. We were either short or didn’t make the right pass or the touch wasn’t quite right. So we just didn’t play a good game technically.”
Rodgers’ Celtic sides have been on the end of similar defeats in the Champions League in the past but he is not minded to change their approach.
“We went in high in confidence,” he said. “The team’s been playing ever so well. So we felt we were in a really good place. But I think we needed to start the game much better than we did.
“When we analyse the game, there were certain issues, positioning, that we would have to be better in.
“We got punished for passes and loose bits of play. It was absolutely ruthless in the finishing. It was actually incredible to see.
“At times our positioning was a little bit too open and you’ve just got to really tighten the game or else they play through you, and that’s what they did.
“Once they’re in then that speed and power that they have at the very highest level, then you see where it takes them.”
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