The Italian striker scored his fifth goal in three league appearances, firing the ball into the top corner four minutes from time after Lorient's Benjamin Moukandjo had cancelled out Ricardo Pereira's early opener.
Balotelli, who joined from Liverpool on a free transfer during the close season, was then sent off two minutes into added time for picking up a second yellow card.
Nice started brightly and converted their first opportunity after 11 minutes, Pereira finding the back of the net with a low shot after being set up by Mathieu Bodmer.
The visitors threatened through Jimmy Cabot but keeper Yoan Cardinale stayed alert.
Moukandjo levelled in the 61st minute with a chip after collecting Mohamed Mara's through ball.
Balotelli unleashed a fine shot from the edge of the box into the opposite top corner shortly before being sent to the dressing room following a brief scuffle with Steven Moreira.
Nice have 20 points from eight games and lead neighbours Monaco, who demolished Metz 7-0 on Saturday, by one point. French champions Paris St Germain, who beat Girondins de Bordeaux 2-0 on Saturday, are third on 16 points.
Olympique Lyonnais beat arch rivals St Etienne 2-0 at home with goals by Sergi Darder and Rachid Ghezzal either side of the interval to move up to fifth on 13 points, leaving Les Verts in ninth place one point behind.
In their 2,368th game in the top flight -- tying Sochaux's record -- Olympique de Marseille were held to a 1-1 draw at Angers as Pierrick Capelle cancelled out Florian Thauvin's opener in stoppage time.
OM are 14th on nine points.
(Editing by Clare Fallon)
