The home side defended well throughout, but they were unable to break down OM until the death, when striker Roux stooped low to send a diving header beyond Steve Mandanda.
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Following the restart, Marseille nearly ended Lille's 11-game streak of not conceding, but somehow the ball stayed out as Valbuena's effort pinballed in the penalty area.
Enyeama then came to rescue for his side just after the hour mark when he made a double stop to deny Florent Thauvin and Dimitri Payet.
However, with the game seemingly heading for a draw, Roux struck his sixth of the season to send Lille to within a point of Paris Saint-Germain at the top of Ligue 1.