Lille's French title defence received a significant setback on Sunday as their 17-game unbeaten run came to an end in a 2-0 defeat at resurgent Marseille in which Loic Remy claimed both goals.
Rudi Garcia's side had not been beaten in the league since a 1-0 loss at home to Montpellier on August 14 but Remy's brace gave Marseille a win that lifted the victors up to sixth and left Lille seven points behind leaders Paris Saint-Germain.
Having won just once in their first 10 league games, OM have now reeled off five straight victories in all competitions and find themselves only two points behind third-placed Lille in the standings.
"It's a huge satisfaction, in terms of the week we've had," said Marseille coach Didier Deschamps, whose side beat Caen in the League Cup quarter-finals on Tuesday.
"Don't forget we were playing a Lille team who were unbeaten away from home, even though they were missing some attacking players."
Lille were aggrieved by an early foul on Eden Hazard by Alou Diarra on the edge of the hosts' box that went unpunished, but that aside, Marseille were much the better team in the first half.
Goalkeeper Mickael Landreau came to Lille's rescue in the 21st minute, saving with his legs after Mathieu Valbuena had released Remy, while only an instinctive block from Aurelien Chedjou prevented Remy from breaking the deadlock moments later.
Benoit Cheyrou threatened twice in quick succession prior to the break, but Landreau parried his stinging drive and when Valbuena turned the loose ball back into the box, he could only find the side netting.
Hazard freed Ireneusz Jelen in the early stages of the second half, but his tame shot was saved by Steve Mandanda.
Deschamps introduced Brazilian forward Brandao from the bench moments later and he received a rousing reception from the OM fans despite facing rape charges in France over an incident near Aix-en-Provence in March last year.
The first goal arrived in the 61st minute and Valbuena was the source, standing up a cross to the back post for Remy to crash home his eighth goal of the season - his sixth with his head and his fifth from a Valbuena assist.
Hazard came close to an instant response but after cutting inside the sliding Nicolas N'Koulou, he planted his left-footed shot straight at Mandanda.
Tottenham coach Harry Redknapp was present at Stade Velodrome to watch Remy and the former Lyon striker enhanced his reputation further in the 83rd minute when he beat Landreau to a loose ball before rolling home his second goal from 20 yards.
On Saturday, Carlo Ancelotti enjoyed a memorable home debut as PSG coach after his side beat Toulouse 3-1 at Parc des Princes to preserve their three-point lead at the top of the table.
Brazilian forward Nene scored twice, either side of a fine goal by record signing Javier Pastore, which was his first strike in the league since October 29.
"It was important for me as it was my first time at the Parc des Princes, so I am very happy," said Ancelotti. "The whole team concentrated and defended as a unit. Pastore and Nene have quality in spades and play for the team."
A 62nd-minute goal from Ligue 1's top scorer Olivier Giroud was enough for Montpellier to beat fourth-placed Lyon 1-0 and remain on PSG's tail in second place.
At the other end of the table, bottom club Ajaccio overcame the first-half dismissals of Samuel Bouhours and Arnaud Maire to beat 10-man Auxerre 2-1 and record their fourth consecutive win in all competitions.