The France international struck twice off the bench to seal victory, but a red card shown to Le Crom ensured PSG were without a goalkeeper for the remainder of the game
The Ligue 1 champions took the lead thanks to Zlatan Ibrahimovic's early second-half effort, before two strikes in quick succession from Kevin Gameiro, against his former club, handed the capital club a commanding victory.
Towards the end of the game however, PSG found themselves in the unusual situation of having used both goalkeepers when Ronan Le Crom was sent off. Mamadou Sakho donned the goalkeeper's jersey but was unable to stop Arnaud Le Lan's penalty.
Carlo Ancelotti, in what is rumoured to be his final game in charge of the champions, fielded a weakened team, with the likes of Siaka Tiene, Alphonse Areola and Zoumana Camara starting. For Lorient, former Barcelona and PSG star Ludovic Giuly was handed a start in the final game of his glittering career.
And Giuly almost got the hosts off to a positive start with an early chance to test Areola in the visitors' goal, before Clement Chantome - one tipped to quit the Parc des Princes this summer - curling an effort past Fabien Audard.
With the league title sown up, and Lorient safe in midtable, there was nothing to play for and this reflected in the standard of play in the first half, with few chances of note produced by both sides.
Nevertheless, young Areola, making his first Ligue 1 start for the club after coming on as a second half substitute in the win against Stade Brestois last week, was made to keep busy in the face of a dangerous Lorient attack.
Maxime Barthelme combined well with Giuly, who teed up Fabien Robert with a deft pass, but the latter's first-time effort was thwarted by a fine save from the 20-year-old goalkeeper.
At the other end, the visitors themselves had chances, but poor finishing ensured a goalless score at the break. First, Zlatan Ibrahimovic headed wide after a fine build-up, before Javier Pastore spurned a great chance, firing wide, despite having Kevin Gameiro in space across goal.
Nevertheless, the visitors stepped up after the break, and duly took the lead within five minutes of the restart.
Gameiro produced a fine run and delivery from the right, as he located Ibrahimovic ahead of Lamine Gassama, with the Swede diverting the ball past Audard from close range to seal his 30th league goal of the season - equalling the record set by Olympique de Marseille's Jean-Pierre Papin in 1989-90,
But Lorient weren't to be outdone, with Giuly continuing to turn back the clock with an energetic performance on his swansong. Immediately after falling behind, he rifled a shot into the side-netting after fine work by substitute Enzo Reale.
However, the Lorient resistance ended there, as PSG hit top form after the hour with two goals in quick succession. First, Ibrahimovic dribbled past Gassama to find Gameiro, who tapped into an empty net for 2-0.
Two minutes later, Gameiro grabbed his second, against his former club with a fine shot, rifled into the bottom corner past Audard, after a great build-up from Tiene for 3-0.
Christian Gourcuff's men continued to push and search for a goal, and were twice denied by substitute goalkeeper Ronan Le Crom, PSG's fourth-choice custodian, who replaced Areola. The veteran denied Yann Jouffre with a fine save, tipping the ball over the bar.
Late drama ensued however, as Le Crom was sent off for a challenge in the box on Julian Quercia. With Ancelotti having used both goalkeepers, it was up to Sakho to go between the sticks, but he was unable to prevent Le Lan's penalty from going in, as the game ultimately ended 3-1.