Gomis, pictured celebrating in style, scored a deserved goal for Lyon in the 57th minute when he lobbed goalkeeper Alexis Thebault from a neat Steed Malbranque pass.
Lyon have 18 points from nine games, one behind leaders Paris St Germain and Marseille, who could reclaim top spot if they do not lose at basement side Troyes later (1900). Brest are 14th with 10 points.
The hosts dominated throughout the match but struggled to hit the target - a Jimmy Briand header struck the crossbar on 33 minutes - until Gomis earned them a deserved victory.
Earlier, Ajaccio drew 0-0 home with Bastia in a tense Corsican derby marred by incidents on and off the pitch.
The two sides were reduced to 10 men each after a mass brawl followed a tough challenge for the ball between Gael Angoula and Johan Cavalli, who were both dismissed seven minutes from time.
The referee had to stop the game for five minutes as the tension spread to the stands where both teams's fans threw fireworks.
Bastia are 12th on 11 points, one ahead of 13th-placed Ajaccio.
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