Dejan Lovren and Lisandro Lopez scored in each half to take Lyon to 13 points, one ahead of Olympique Marseille who visit AS Nancy later (1900). Ajaccio are 14th.
Lyon struggled to create chances 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 a couple of 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 halftime.
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 pegged one back for the hosts who had Cheick Diarra sent off for a dangerous tackle on Traore with 11 minutes left.
Lorient are third on 11 points from five games and Rennes, who suffered their fourth defeat, are 18th.
- Lisandro Lopez
- Adrian Mutu