Cengiz Under forced a good save from Lorient goalkeeper Vito Mannone in the first half but Marseille struggled to create chances as their eight-match winning run away from home ended.
"It's disappointing. The match was within our grasp but we were a bit lacking when it mattered most," Marseille midfielder Matteo Guendouzi told Prime Video.
Former Marseille striker Bamba Dieng went close to scoring against his old club but was denied by Pau Lopez on the hour as Igor Tudor's side dropped two points behind second-placed Lens. 
"There's no pressure, there's still a lot of matches," said Guendouzi.
Marseille also missed the chance to further distance themselves from Monaco, who were held 2-2 at Nantes earlier in the day.
Axel Disasi lashed Monaco ahead on 21 minutes and Eliot Matazo got his team's second when Nantes goalkeeper Alban Lafont flapped at a corner and the ball trickled in off the Belgian midfielder.
But Egypt international Mostafa Mohamed headed Nantes back into the game midway through the second half before fellow substitute Ludovic Blas nodded in an equaliser at the far post.
                  - Lyon recover from cup pain -                                    Lyon bounced back from their stinging midweek loss at Nantes in the French Cup semi-finals as they came from behind to beat Rennes 3-1.
After winning 1-0 at Paris Saint-Germain last weekend, Lyon's hopes of silverware this season were dashed when Blas got the only goal for Nantes to keep the holders on track to retain the cup.
Laurent Blanc's side trailed against Rennes as Amine Gouiri struck against his former club, but Lyon recovered in the second half to win a game after going behind for the first time this season.
Corentin Tolisso curled in a sublime long-range shot to haul Lyon level and Alexandre Lacazette's 18th goal this term soon put the hosts in front.
Young forward Bradley Barcola completed the turnaround with 12 minutes to go, netting for the third time in four games to help Lyon stay in sight of a place in the Europa Conference League.
"You always have to believe," said Blanc. 
"The last match of a series of three in a week is often the most physically difficult to play and after
Wednesday's (French Cup) disappointment, the first half could be explained by mental fatigue.
"Rennes took advantage of it and could have taken advantage of it more. I am very satisfied especially since I was angry at half-time." Auxerre dragged themselves out of the bottom four with a 3-0 win at Ajaccio, whose coach Olivier Pantaloni said afterwards his team were all but doomed to relegation.
"The team was disastrous. We didn't deliver and this loss condemns us to Ligue 2. Given our schedule, I don't see how we're going to manage."
Folarin Balogun's stoppage-time penalty -- his 18th league goal of the campaign -- salvaged a 1-1 draw for Reims against Brest.
Toulouse won 2-1 at Montpellier and Clermont pushed Troyes closer to the drop with a 2-0 away victory.