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.
De Zerbi dubbed Saturday's win "a significant response in terms of (his side's) character".
"We managed to shake off that defeat to Auxerre, which really hurt us," he added.
The Italian will be hoping his side further prove him right next week when they welcome second-placed Monaco to the Velodrome.
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.
VAR drama
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 -- the set-piece stemming from the foul that caused Lens' leveller to be ruled out.
Elsewhere, Lyon and Reims passed up the opportunity to go fourth with a 1-1 draw in the Champagne region.
"For us I think it's two points dropped," Lyon captain Alexandre Lacazette told DAZN.
"Our problem this season has been starting slowly in the second half and we paid for it again here," the ex-Arsenal striker added.
Rayan Cherki gave Lyon the lead seven minutes before the break but Oumar Diakite struck back for the hosts in the 55th minute.
The result leaves Lyon provisionally level on 19 points with fourth-placed Lille, with Reims one point back in sixth.
Saint Etienne ground out a 1-0 win at home to Montpellier in an encounter that could very well already have implications on the relegation battle come the end of the season.
Benjamin Bouchouari's 47th-minute strike sent Les Verts up to 13th place, while Montpellier remain rooted to the foot of the table with just two wins from 12 matches this term.
On Sunday, Lille can move ahead of Lyon when they welcome struggling Rennes and Strasbourg visit Nice.
