The capital club, who emerged from a string of frustrating seasons to finish sixth last term, had looked like title contenders in their first few matches of the campaign.
Last weekend, however, they collapsed in the last five minutes at Monaco, conceding two late goals to lose 2-0 and drop to fifth place, three points off the lead.
The match was stopped for a few minutes after Paris fans let off flares and fireworks and the club, who have struggled for years to keep a handful of troublesome supporters under control, now face disciplinary action.
To make matters worse, Benin midfielder Stephane Sessegnon, arguably PSG's best player, was sent off for a nasty challenge in the closing stages and will be suspended for the match against Lyon on Sunday.
"Moments like these are difficult to handle," said Brazilian defender Ceara, aware PSG need to bounce back straight away.
"Even without Stephane, we will play a great match against Lyon," Ceara told reporters. "Everybody's waiting for that one. I believe we can live up to it and beat Lyon."
Lyon, who beat Fiorentina 1-0 in a Champions League group match on Wednesday, won seven French titles in a row before losing their crown to Girondins Bordeaux last season. They have started well with four wins and a draw and are in second place, level with leaders Bordeaux with 13 points from five games.
"They are having a good run but we're ambitious and we must win our home games, no matter who we face," Ceara said.
Bordeaux, who began their Champions League campaign with a 1-1 midweek draw at Juventus, face a seemingly easier task when they visit promoted Boulogne on Saturday.
Surprise package Montpellier, in third spot on their return to the top flight, will be tested on Saturday at fourth-placed Olympique Marseille who also have 11 points.
