A win on Sunday would have moved Marseille level on points with the defending champions, but instead third-place Marseille dropped six points behind unbeaten PSG and stayed three points behind Monaco in second spot.
The humiliating manner of the defeat will doubtless test the patience of Marseille's hugely demanding fans.
Some of them started leaving Stade Velodrome before the end of the first half and the players were jeered off the field at the end. Aside from careless mistakes, a lack of leadership was evident.
Marseille did not qualify for any European competition this season and their players were fresh while coach Roberto De Zerbi had a full squad available.
Former PSG midfielder Adrien Rabiot started in midfield for Marseille, but the visitors were far sharper and took the lead in the seventh minute through midfielder João Neves following a low cross from left back Nuno Mendes.
Things got worse for Marseille when midfielder Amine Harit was shown a straight red card in the 20th for a high challenge on PSG captain Marquinhos.
Although television replays showed Harit did not raise his leg higher than the midriff of Marquinhos, the decision was maintained.
A dreadful own-goal from central defender Leonardo Balerdi gifted PSG a goal in the 29th. A cross came in with no PSG player in the penalty area, yet Balerdi stuck his leg out and prodded the ball past his stranded goalkeeper Geronimo Rulli.
Balerdi was caught napping on the third goal when he failed to close down winger Bradley Barcola, who swept home after Ousmane Dembélé's shot was saved and the ball came back into the area.
PSG controlled the game in the second half but did not appear to push for another goal, which may frustrate coach Luis Enrique given his side's problems scoring in the Champions League.
A lack of composure also penalised Monaco earlier, when Vanderson was sent off in a 2-1 defeat at Nice.
Monaco led through Switzerland striker Breel Embolo's 39th-minute strike as he latched onto Maghnes Akliouche's defence-splitting pass for his second goal in six days.
After Evann Guessand equalised with a fine downward header in first-half stoppage time, Vanderson picked up a second yellow card moments later following an altercation with forward Mohamed-Ali Cho.
A terrible backpass from Krépin Diatta gifted Nice a second goal as striker Gaëtan Laborde latched onto it and neatly clipped the ball over the goalkeeper in the 71st.
Auxerre hit back twice to earn a 2-2 draw with Lyon, with central defender Sinaly Diomandé and midfielder Hamed Traoré both scoring for the second straight game.
Georges Mikautadze, who starred for Georgia at the European Championships earlier this year, grabbed both of Lyon's goals.
Rock-bottom Montpellier lost 3-0 at home to Toulouse, one week after being routed 5-0 by visiting Marseille.
Montpellier changed coaches between the matches, with Michel Der Zakarian fired and Jean-Louis Gasset hired.
But fans at Stade de la Mosson watched another horror show as Toulouse went 3-0 up inside 30 minutes. Zakaria Aboukhlal scored twice and strike partner Joshua King made it 3-0, having earlier had a goal ruled out.
Also, Brazilian midfielder Andrey Santos scored twice as Strasbourg beat Nantes 3-1 at home to move up to midtable.
