The Dutch champions were soundly beaten 4-0 at home by the Premier League giants on a thoroughly disappointing night for Feyenoord.
Goals from John Stones (2), Sergio Aguero and Gabriel Jesus gave City the convincing win in the Group F opener to leave the Eredivisie side with plenty of work to do to qualify for the knockout stage.
Van Bronckhorst admitted his side had been poor but he also acknowledged City were a class above.
He said: "I thought that we were really disappointing especially in the first half. I was aware that for a few of my players that it was their first time playing at this level playing against one of the best teams in Europe.
"We knew that we had to grow into the game and gain confidence and to be 1-0 down after only two minutes was frustrating. Manchester City are a good team and everybody knows that they achieve results beating teams by many goals quiet regularly."
He added: "I told my players that I remember playing for Feyenoord in the 90’s when we were 3-0 down to Juventus within 30 minutes and that the Champions League is another level in terms of speed and intelligence.
"We must be critical about our performance tonight. We were tense tonight and nobody has to have any sympathy with us. The difference was too big tonight facing a team who’s squad is valued at more than 800 million euros.
"The difference in quality was too big tonight and that is why we did not win tonight. We knew that we are in a tough group along with Napoli and Shakhtar Donetsk."