Second-half strikes from Valentin Rongier, Luis Henrique and Pierre-Emile Hojbjerg ensured Marseille remain third, nine points behind PSG and three off Monaco in second spot.
After the top two both won on Friday, Marseille needed to get back to winning ways with their trip to Lens following their slump in form before the international break and anything other than a win would have meant they trailed PSG by at least 11 points.
Following a flying start to life under new coach Roberto De Zerbi, Marseille have been hit-and-miss in recent weeks, losing two of the their last five in the league.
These came in the form of a chastening 3-0 loss at home to arch-rivals PSG in October and then in the last matchday before the break, a surprise 3-1 home defeat to mid-table Auxerre.
Lens looked the more threatening side in the first half with Marseille relying on goalkeeper Geronimo Rulli to keep the match goalless going into half-time.
However, it was the south-coast side that eventually made the breakthrough four minutes into the second period through Rongier.
Good centre-forward play by Neal Maupay set up the chance for the midfielder who supplied a cool finish one-on-one with the goalkeeper.
On 57 minutes, Luis Henrique doubled the visitors' lead with a rolled finish from the right-hand side of the box after a swift counter-attack caught Lens on the break.
But everything seemed to unravel for Marseille in the space of five minutes at the end of the match.
Angelo Fulgini pulled one back for Lens in the 80th minute, before Remy Labeau Lascary thought he had grabbed a leveller on 85 minutes.
However, the home supporters' joy was cut short when the referee decided after a VAR review that there had been a foul in the build-up and the equaliser was disallowed.
Let off the hook, Marseille then sealed the three points one minute from time when Hojbjerg drilled home a fierce free-kick from the edge of the box.
Later on Saturday, lowly Saint-Etienne host bottom-of-the-table Montpellier before Reims take on Lyon.
