With one eye on Wednesday's Champions League trip to Barcelona, PSG coach Carlo Ancelotti opted to rest several star names - including David Beckham, Javier Pastore, Ezequiel Lavezzi and Lucas Moura - from his starting line-up.
Despite that, second-half goals from Menez and Zlatan Ibrahimovic - the latter teed up by substitute Beckham - proved enough to claim all three points and keep the capital club a healthy distance clear of second-placed OM, who beat Bordeaux 1-0 on Friday night.
But Menez insisted after the game that nobody at the club would be getting carried away with their lofty position just yet.
"The title is not yet acquired and must stay focused," he said on www.psg.fr. "But it is true that this victory is important.
"At the break, the coach asked me to step it up. I saw that there was space in front of me and I knew I would enjoy it. I am pleased to score, but it is the victory that is most important.
"The group is working quietly. When everyone is fighting, we see a beautiful Paris St Germain."
Ancelotti, whose side drew 2-2 at the Parc des Princes in the first leg of their Champions League quarter-final on Tuesday, was pleased with how his side performed following their midweek exertions.
"After the match against Barcelona, we knew that this meeting in Rennes would not be easy," the Italian said. "This match was important as Marseille won on Friday.
"I made some changes because I wanted a fresh team on the pitch. We played well for the first 60 minutes before having more difficulties in the last half-hour because of a lack of energy.
"This is a very important victory, which allows us to move a step closer to the title."