A deflected strike from Lyon's Cameroon international Clinton N'Jie with 13 minutes remaining at Stade du Moustoir cancelled out Jordan Ayew's second-half opener.
The result - the third straight draw between the two teams at Lorient - left Lyon two points clear of Marseille and defending champions Paris Saint-Germain after 25 matches.
Lyon came into the fixture on the back of consecutive draws against Monaco and PSG, but Hubert Fournier's men were expected to see off the challenge of Lorient, who hover just two points above the relegation zone.
However, Lorient had other ideas as Ghanaian substitute Ayew put the home side ahead in the 50th minute - just minutes after his introduction in the second half.
Ayew, who replaced Rafidine Abdullah at the break, tapped home the opener from Benjamin Jeannot's cross.
Lyon went in search of an equaliser and were rewarded in the 77th minute, with N'Jie firing the ball underneath Lorient goalkeeper Benjamin Lecomte, who was unable to keep it out.
Bordeaux moved within a point of fourth-placed Saint-Etienne after winning 1-0 at Stade Jacques Chaban-Delmas.
Greeted by a sea of colours as fans threw coloured powder at each other in the stands, a long-range strike from Uruguayan forward Diego Rolan gave Bordeaux back-to-back league victories.
Bordeaux are now within touching distance of Saint-Etienne, who occupy the UEFA Europa League spot.
Meanwhile, Guingamp defeated rock-bottom Metz 2-0 away from home at Stade Saint-Symphorien.
First-half goals from Christophe Mandanne and Jeremy Pied helped Guingamp up to eighth.
