Jordan Ayew's header in the 54th minute lifted a dominant Marseille to 15 points from five games, two ahead of Olympique Lyon who beat Ajaccio 2-0 thanks to goals in each half by Dejan Lovren and Lisandro Lopez.
Alain Traore's splendid double earned nine-man FC Lorient a 2-1 win at neighbours Stade Rennes left them third on 11 points.
Marseille, who had never previously won their five opening league matches, outclassed their lowly hosts in the first half but lacked sharpness.
"We should have been one, two or three goals ahead at halftime because we had the chances," coach Elie Baup told French channel Canal Plus.
"This is the way I want us to play."
Striker Andre-Pierre Gignac had four clear-cut chances but he either missed the target or was denied by goalkeeper Guy-Roland Ndy Assembe.
Andre Ayew shot past Ndy Assembe in the 11th minute, only to see defender Vincent Muratori stop the ball on the goal line.
Marseille kept creating chances after the break and Ayew eventually put them in front when he netted a powerful header from the penalty spot after his brother Andre's cross.
Nancy tried to mount a comeback without really threatening Marseille and lie 17th in the standings on four points.
Second-placed Lyon struggled to create chances against Ajaccio until centre-back Lovren put them in front when he headed home Clement Grenier's corner kick in the 25th minute.
The seven-times French champions tightened their grip on the match but Bafetimbi Gomis twice shot narrowly wide.
Ajaccio goalkeeper Guillermo Ochoa made two great saves after the break, parrying Grenier's fine lob and stopping a point-blank Gomis header.
Boosted by Romanian striker Adrian Mutu, who came off the bench to make his Ligue 1 debut, Ajaccio pushed hard to level, only for Lopez to double the advantage after a lightning counter-attack on 75 minutes.
"We knew it would be difficult. We tried to do our best but unfortunately, we did not get a point," Mutu told French channel Canal Plus.
"I am very confident I'll soon be in better shape."
In Rennes, Traore put the visitors ahead in the 23rd minute with a stunning shot from 30 metres and doubled his side's lead with a free-kick from the same distance minutes before half-time.
Lorient, who had defender Maxime Baca sent off after 32 minutes for a rough challenge on Jonathan Pitroipa, were reduced to nine early in the second half when goalkeeper Fabien Audard was shown a red card for fouling Pitroipa.
Pitroipa pulled one back for the hosts who had Cheick Diarra sent off for a dangerous tackle on Traore with 11 minutes left.
Rennes's fourth defeat of the season left them languishing in 18th place in the table.
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