Many thought holders Bayern would brush aside a faltering United in the first leg at Old Trafford on Tuesday, but David Moyes' men held their own and earned a 1-1 draw to take to Munich next week.
Despite the two sides' differing fortunes so far this season - Bayern have already retained their Bundesliga title, while United sit seventh in the Premier League - Sammer insists he knew the tie would be no straightforward task.
"We sounded a warning ahead of the game in Manchester but people turn a deaf ear at times," he said.
"They played just as we expected. They were very strong physically, organised and they tried to play on the counter.
"They managed that really well and they made life difficult for us.
"But that’s what you expect in the Champions League - it's the top level of the game. So we accept it and we’re happy with the result."
