Monaco and Toulouse were both away winners while Racing Strasbourg and Olympique de Marseille won at home on the opening weekend of the new French season.
Champions PSG, with former Spain coach Luis Enrique in charge for the first time and featuring six debutants, were held to a 0-0 stalemate by Lorient in an uninspiring start to the defence of their title.
But the outing was overshadowed by the absence of Kylian Mbappe, who had been in a contract stand-off and not trained with the squad. However, he did return to training on Sunday after what PSG called "very constructive and positive discussions".
Lens, who finished a point behind PSG last season, were 2-0 up inside 22 minutes at Brest on Sunday but went on to lose 3-2 as Romain del Castillo netted two penalties for the hosts.
Rennes substitute Ibrahim Salah scored twice in the six minutes in which he played, adding to goals scored by Arnaud Kalimuendo, Amine Gouiri and Jeremy Doku as last season's fourth-placed side got off to an impressive start.
Patrick Vieira's tenure as coach at Strasbourg began on a winning note as second-half goals from Jean-Ricner Bellegarde and South African international Lebo Mothiba saw them overcome Lyon 2-1.
Wissam Ben Yedder netted twice as he captained Monaco to a 4-2 success at Clermont Foot. It was new coach Adi Hutter's first game in charge of the principality club.
Toulouse, who thrashed Nantes 5-1 in last season's French Cup final, added more salt to the wounds as Rasmus Nicolaisen's header from a corner in added time snatched a 2-1 away win.
Also on Sunday, there was a late equaliser for Le Havre, last season’s Ligue 2 champions, as they held Montpellier 2-2 away.
On Saturday, Olympique de Marseille put their 1-0 midweek loss in a Champions League third qualifying round, first leg at Panathinaikos behind them to beat visiting Stade Reims 2-1 as they came from behind with Vitinha netting the late winner.
