The champions, who ended Olympique Lyon's seven-year reign last season and enjoyed a nine-point lead before Christmas, still top the table on 51 points with two games in hand but are only ahead of promoted Montpellier on goal difference.
The postponement of their last two league games, run to the League Cup final against Olympique Marseille on March 27 and return leg of the Champions League last 16 tie with Olympiakos, which they lead 1-0, means they face a gruelling schedule.
"I always said we could only play better. We are going through a very good phase and some people could be on for a big surprise," international defender Jean-Alain Boumsong told reporters after Lyon beat Nice 2-0 last weekend.
"This sequence of good results has brought us confidence but we have to keep up the rhythm until the end of the season," said coach Claude Puel.
PSG are now 12th on 33 points and in crisis after one of their fans suffered a life-threatening head injury in a fight between rival groups of supporters before Sunday's kick-off.
Chairman Robin Leproux said on Tuesday that "a new level of urban guerrilla warfare" had been reached and has ordered the club to stop selling tickets to supporters for away games.
