Brazilian centre back Alex scored in the 87th minute to cancel out Mustapha Yatabare's 84th-minute opener in a lively encounter at the Roudourou stadium.
PSG, who were knocked out of the French Cup by Montpellier on Wednesday, lead the table with 51 points from 22 games ahead of Monaco who host fifth-placed Olympique Marseille on Sunday.
Three days after a 2-1 home defeat in their last-32 Cup game, Laurent Blanc's PSG side barely threatened the hosts.
"It was hard to play on that pitch, which was in very bad shape," PSG keeper Salvatore Sirigu told Canal Plus.
"But they played with their heart. It's important to leave Guingamp with one point."
PSG were below their best without Argentine forward Ezequiel Lavezzi and Brazil centre back Thiago Silva, who were suffering from groin and ankle injuries respectively.
Guingamp had the best chance of the first half when Rachid Alioui's 20-metre missile was deflected on to the bar by Sirigu on the stroke of halftime.
Seconds later, Marquinhos brought down Yatabare in the penalty area but referee Said Ennjimi waved play on.
Argentina international Javier Pastore, who started on the left of the PSG attack in place of Lavezzi, failed to shine and was replaced in the 68th minute by Lucas.
The Brazil forward brought speed but no ideas to the visitors' game.
Yatabare opened the scoring six minutes from time when he beat Marquinhos to the ball to head home from a corner, only for Alex to equalise three minutes later.
On Friday, third-placed Lille, who are on 41 points, were held to a 1-1 draw by visitors Stade Rennes.