The Parisians were held to a 1-1 draw at Lorient while the Bretons lost 2-1 at Auxerre.
Brest are top on 22 points but only eight points separate them from bottom but one Nancy in 19th leaving a lot of teams still in the race for the title.
They include Lyon who beat Nice 1-0 on Sunday night to jump to eighth on 19 points. PSG are fourth on 20 points, level with Rennes in fifth, but two points behind promoted Brest who retain the lead after a 1-1 draw at home to Sochaux on Saturday.
In Lorient, PSG dominated the first half and created plenty of chances but the home goalkeeper Fabien Audard produced some stunning saves and strikers Guillaume Hoarau and Mevlut Erding remained ineffective.
Lorient's Lynel Kitambala, unmarked at the far post, opened the scoring in the 32nd minute following a corner, before Nene grabbed the equaliser in the dying seconds after a free-kick.
"We have a lot of regrets about our first half where we had a lot of dangerous chances and then we conceded a stupid goal... fortunately we equalised at the end," PSG midfielder Clement Chantome told Foot Plus TV.
"It is a shame that we conceded a goal, we were not vigilant enough. There were only a few minutes left," Lorient defender Gregory Bourillon said. "But overall the draw is a logical result."
Auxerre owed their victory to a perfectly curled shot from Valter Birsa on 67 minutes and a late winner by Julien Quercia on a counter-attack after Rennes had equalised through Jires Kembo-Ekoko.
In Lyon, Jeremy Pied put the home side ahead on 30 minutes. Claude Puel's men then missed the opportunity to double the lead when Michel Bastos wasted a penalty generously awarded by the referee after Bafetimbi Gomis seemed to trip over himself in the box.
"Today our mission is to take points. We are not where we should be yet but the important thing is to win", Lyon and France midfielder Yoann Gourcuff said.
"It is a bizarre championship, a very tight league. It is very peculiar."
