Cavani, who took a couple of matches to settle after joining the Qatari-backed club from Napoli for a French record 64 million euros (£54.2 million), then showed he has recovered his scoring touch to reach seven goals in his last six league games.
The Uruguay striker headed PSG's third from a Lucas cross just before halftime and added the fourth with nine minutes left. He is now the top scorer in the French league with nine goals, one more than Monaco striker Radamel Falcao.
Big-spending PSG, who are unbeaten in all competitions since March, have 28 points from 12 games, three ahead of Monaco who visit third-placed Lille, on 23, on Sunday. Lorient stay just outside the relegation zone in 17th place with 10 points.
They were missing injured striker Zlatan Ibrahimovic while regulars Blaise Matuidi and Ezequiel Lavezzi started on the bench ahead of Tuesday's Champions League game at home to bottom side Anderlecht in Group C which they lead by five points.
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