The capital side have 38 points from 14 games and lead second-placed Olympique Lyonnais, who slumped to a 3-0 defeat at Nice on Friday, by a massive 13 points after a routine win.
League top scorer Benjamin Moukandjo reduced the arrears late on as Lorient stayed seventh on 20 points.
There was a release of doves and a minute's silence before kickoff to honour the 130 victims of last week's Paris attacks on bars, restaurants, a concert hall and a football stadium.
"France suffers but does not die," read a banner in the stands at Lorient's Stade du Moustoir, where the crowd sang the French national anthem.
The Marseillaise was played in all stadiums in France on the first round of Ligue 1 matches since the attacks.
"It's a good result, we're on a good run," PSG coach Laurent Blanc said. "Even if the context was tough, as you know, we can be satisfied tonight. But I'm eager to get back to Paris and be with my family."
With PSG comfortably top of the league, Laurent Blanc gave Ongenda his first start this season and the 20-year-old striker did not disappoint in the absence of the injured Angel Di Maria, David Luiz, Marco Verratti, Javier Pastore and Ezequiel Lavezzi.
He tapped the ball home in the 26th minute from Gregory van der Wiel's cross as the visitors took a deserved lead.
Ongenda then played a one-two with Zlatan Ibrahimovic whose cross was netted by Matuidi from point-blank range in the 32nd.
Moukandjo leapfrogged Ibrahimovic at the top of the scoring charts by heading home his 10th goal of the season from Romain Philippoteaux's cross.
In Corsica, the Bastia v Gazelec Ajaccio game was called off because of gusty winds and will be played on Sunday, the French League said in a statement.
Monaco climbed up to fifth on 23 points when Croatian Mario Pasalic's first-half strike gave them a 1-0 home win against Nantes.
On Sunday, Caen will move up to second if they beat visiting Angers before St Etienne take on Olympique de Marseille in the evening match.
(Reporting by Julien Pretot, editing by Ken Ferris and Ian Chadband)
