Roux put coach Rene Girard's side ahead in the 14th minute with his second goal in three games, and the 19-year-old Traore sealed the win in the last minute.
The victory moved Lille provisionally up to seventh place, four points behind sixth-place Bordeaux, although Montpellier only needs a draw against Caen later Sunday to reclaim seventh place.
In Sunday's late match, Lyon needed to beat bitter rival Saint-Etienne to move back to the top of the league ahead of Paris Saint-Germain.
Injury-hit PSG won 3-1 at Nice on Saturday to keep the pressure on Lyon in the close-fought title race.
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