The Blues suffered their first home defeat in 29 group stages matches after surrendering a half-time lead to lose 2-1 against the Swiss champions.
|14/1||Chelsea are 14/1 with William Hill to win the Champions League this season
'It was a very tough game, an open game,' The Serb told the club’s official website. 'We had a lot of runs in the first half, and scored in a very good moment.
'We tried to kill the game in the second half and unfortunately the opposite happened. We conceded the first one, which was difficult for us, and after that we started to do different things.
"We weren't ready for that moment and we then conceded the second one to lose the game.
"We have to stand up and show the character for the other games because we can't go back and have to look forward."
With five games still left to play in Group E, Ivanovic believes Jose Mourinho’s men can use the setback to spur them on, starting with a trip to Steaua Bucharest at the beginning of October.
"It's a bad start in the Champions League but it's just the first game," he continued.. "We have to stand up, show the character in other games and this situation has to be a good example for the future."