Djamel Bakar had an early chance to give Nancy the lead, but his powerful strike was saved by the goalkeeper.
Romain Grange had another chance for the home side on 14 minutes, but his effort was well off target.
Kevin Monnet-Paquet came close to giving Lorient the advantage on 20 minutes, but he could not find the finish to give his side the lead.
Paul Aloo Efoulou then put Nancy ahead on 36 minutes, finishing expertly from a Grange assist.
Three minutes into the second half, Grange came close to doubling his side's advantage, but his effort flew past the post.
Jeremie Aliadiere then levelled the scores after 50 minutes.
Sebastien Puygrenier finished expertly on 71 minutes to restore the home side's advantage and secure the win.