"This victory is dedicated to our amazing fans. This match was crucial for them and for solidifying our position in the table."
Joao Neves gave the visitors the perfect start early on, before a disastrous 10-minute period just prior to the half-hour saw Marseille lose Harit and ship a second goal when captain Leonardo Balerdi turned into his own net.
Bradley Barcola then tucked away PSG's third, and his eighth of the season.
It was a chastening night for Roberto De Zerbi's Marseille, who had enjoyed a strong start to the campaign and went into the match with the possibility of joining their biggest rivals on 20 points with a victory.
But instead they endured their 12th-straight home match against PSG in the league without a win as hundreds of their fans had already made for the exit by half-time.
"I'm disappointed. We had prepared a match of courage and personality. But up until Harit was sent off, there was neither courage nor personality," said De Zerbi.
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"It wasn't the match we had in mind and that's a problem. We can lose, but when you wear the Marseille shirt, you can't play without personality and courage," added the Italian coach.
Portuguese midfielder Neves made his mark seven minutes into his first Classique when he pounced on a handling error by goalkeeper Geronimo Rulli to open the scoring.
In the 20th minute, the match swung definitively in PSG's favour when Harit was given his marching orders after catching Marquinhos in the stomach with a high boot.
"The sending-off changed the game," said Luis Enrique. "From then on, the match was harder for our opponents and less open."
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As if to compound Marseille's misfortunes, Balerdi doubled the away side's lead nine minutes later as he stretched to cut out a seemingly routine cross and ended up knocking the ball past the advancing Rulli and into the goal.
Barcola put the cherry on the cake for PSG five minutes before the break, finishing after determined build-up play by Ousmane Dembele.
'Two stupid mistakes'
Earlier, high-flying Monaco passed up the opportunity to go top of the table when they lost 2-1 at neighbours Nice.
Breel Embolo gave the visitors a first-half lead before Nice struck back via Evann Guessand and Gaetan Laborde to inflict 10-man Monaco's first loss of the domestic campaign.
The principality side remain in second place on 20 points, three points behind leaders PSG.
"I'm not happy with the result," said Monaco coach Adi Huetter.
"When you lose a derby, everyone is disappointed, that's clear. But we're guilty because we had the game in our hands. And it came down to two stupid mistakes."
Embolo broke the deadlock for Monaco in the 39th minute, finishing neatly after being released by Maghnes Akliouche's through-ball.
But the match turned in first-half stoppage time as Guessand headed in an equaliser for Nice and Monaco's Brazilian defender Vanderson then picked up a second yellow.
A poorly-executed corner routine cost Monaco as Laborde was gifted the opportunity to run through completely unchallenged, before finishing on 71 minutes.
Lyon drew 2-2 at home to Auxerre to move to seventh in the table.
Georges Mikautadze twice gave the hosts the lead but they were on both occasions pegged back by Sinaly Diomande and Hamed Traore.
Strasbourg climbed to the top half of the table by beating Nantes 3-1, thanks to a brace from Andrey Santos and a Dilane Bakwa goal.
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Two goals in the opening 10 minutes by Zakaria Aboukhlal sent Toulouse on their way to a 3-0 win at lowly Montpellier.
(This story has not been edited by staff and is auto-generated from a syndicated feed.)