Fellow attacker Brandao put the visitors ahead in the 17th minute from a neat Renaud Cohade cross and Aubameyang made it 2-0 with a curling low shot five minutes before the break.
Aubameyang's sixth goal in five games - his 14th in the league this season - then sealed victory with two minutes to go.
"I work hard, very hard, and I have been rewarded with these goals," the Gabon international told reporters. "It's also a reward for the team because I cannot score without them."
"I have always said we are chasing third place. We know it will be tough but we hope to keep up this rhythm."
Nancy had Florent Zitte sent off in the 78th minute while St Etienne's Fabien Lemoine was dismissed 14 minutes earlier.
Fifth-placed St Etienne have 44 points from 26 games, one adrift of Nice who beat lowly Stade de Reims 2-0 on Friday.
Nice and St Etienne are chasing Champions League qualification behind third from top Olympique Marseille who travel to Paris St Germain on Sunday when the league leaders could give a debut to former England captain David Beckham.
Second-placed Olympique Lyon, three behind PSG on 48 points, also host Lorient on Sunday.
Champions Montpellier are sixth with 41 points after beating third from bottom Evian Thonon Gaillard 1-0 thanks to a late Younes Belhanda goal.
Montpellier, who made a poor start to the season, have won four of their last five games and leapfrogged Stade Rennes on goal difference after the Brittany side needed a last-gasp goal from Jean Makoun to draw 2-2 at home to struggling Sochaux.
Makoun, on loan from English Premier League Aston Villa, scored following an 88th-minute corner as Rennes rescued a point after having twice trailed.
John Boye headed home in the 34th minute to cancel out Giovanni Sio's opener for Sochaux who then regained the lead with a superb Sebastien Corchia strike in the 56th.
Rennes are one point ahead of 10-man Lille who won 3-1 at Ajaccio.
A Yohann Poulard own goal handed the 2011 champions the lead in the 38th minute and Lille cruised home despite having full back Lucas Digne dismissed for a dangerous tackle on Matthieu Chalme in the 61st.
Dimitri Payet grabbed his ninth and 10th league goals of the season as Lille rose to eighth in the table.
- Sports & Recreation