Jeremy Menez doubled PSG's lead in the 39th minute, driving home Marco Verratti's chipped throughball.
In the absence of Ibrahimovic, Cavani played in his preferred center-forward position and the Uruguayan extended PSG's lead three minutes from halftime. Baptiste Reynet mistakenly came to try and gather a ball but Lucas evaded the substitute goalkeeper and crossed in for Cavani to head into an empty net.
Moments earlier Lorient had had its best chance of the match when PSG goalkeeper Salvatore Sirigu pulled off a stunning save to keep out Kevin Monnet-Paquet's header.
Cavani doubled his tally nine minutes from time. Reynet did well to parry Adrien Rabiot's header but Cavani was on hand to tap in the rebound for his ninth goal of the season.
"The coach asked us to be serious and focused for the first 15 minutes and we conceded in the third," Reynet said. "It's really annoying. We have to quickly regroup and focus on Reims now."
PSG moved provisionally three points clear of Monaco, which visits third-placed Lille on Sunday.