The Blues' convincing defeat leaves the Old Lady requiring just one point against already-qualified Shahktar Donetsk in their final Group F game to prevent the holders from reaching the knockout stages.
"We said before the game we had our destiny in our own hands but not anymore," Cech told reporters after the match.
"Now we have to do our bit to win our last game and hope destiny will be kind to us.
|28/1||Chelsea are 28/1 with Bet365 to lose 3-0 to Manchester City
"It is a very sad moment because last season the Champions League was like a dream. I wouldn't say it's a nightmare but it's a huge disappointment."
The 30 year-old praised the Bianconeri's performance but argued that his team contributed to their own downfall by not being clinical in front of goal.
"I think we showed much better spirit than in the last few games," he continued.
"We did well and created some chances but, in such an important game, if you create chances you have to take them and that was the difference.
"They went ahead with a lucky deflection and the second goal was a deflection as well but they put on a very good performance and they did really well."