Lois Openda continued his hot run of form with the only goal as Lens claimed a 1-0 win at Rennes on Saturday to move second in Ligue 1.
Lens edged above Marseille on goal difference into the second automatic Champions League qualifying place, six points behind leaders Paris Saint-Germain.
Rennes stayed fifth as their inconsistent season continued with a defeat in their first outing since winning 2-0 at PSG before the international break.
Belgium striker Openda nodded Florian Sotoca's cross over the line from close range to score his 15th Ligue 1 goal of the season and sixth in three league games.
Lens survived a scare as Rennes centre-back Warmed Omari had a late effort ruled out for offside.
On Friday, Marseille were held to a 1-1 home draw by Montpellier to miss out on the chance to climb within four points of reigning champions PSG, who host Lyon on Sunday.