Two players were sent off as Stade Francais triumphed 27-23 over Racing 92 on Sunday, in a Top 14 clash between two clubs who appeared on course for a merger earlier in the season.
Club bosses announced the proposed joining of forces in March, but the plans were scrapped following a fierce backlash from players and fans.
And this contest between the Parisian rivals proved fiery, with Pascal Pape and Wenceslas Lauret shown red cards for throwing punches shortly before half-time.
Tied at 13-13 at half-time, Stade soared clear at the beginning of the second half through tries from Djibril Camara and Jonathan Danty.
Ben Tameifuna crossed as part of a Racing fightback, but it was not enough to prevent Stade from pulling level on points with their opponents.
In the day's other match, league leaders La Rochelle held off a spirited Montpellier to win 40-37.
Montpellier scored 21 points in the last 10 minutes but were unable to force their way into the top two.