The Parisians failed to close the gap on Nice at the top of the table after two second-half goals from Guingamp saw them lose a second successive league game
Under-pressure manager Unai Emery suffered another slip up in the Ligue 1 title race as Guingamp recorded a surprise win over PSG.
The visitors struggled to break down Guingamp before Antoine Kombouare's side scored two quickfire goals to shock PSG.
Yannis Salibur broke the deadlock with Nill De Pauw netting four minutes later. Edinson Cavani scored late on, but the Ligue 1 holders could not find a second.