Paris Saint Germain, fresh from progressing to the Champions League quarter-finals, capped a profitable week with a 2-0 win on Sunday night.
The game marked the latest stepping stone on what is becoming a relentless march to the French title extended PSG's unbeaten league run to 13 matches.
Ibrahimovic had PSG deservedly in front in the 14th minute, the Swedish striker rolling the ball in although St Etienne rounded on the referee claiming Matuidi had been offside.
The St Etienne goal continued to be the centre of attention as the hosts dominated, with Ibrahimovic doubling up four minutes from the break, prodding home Edinson Cavani's cross from the left having started the sweet move.
St Etienne emerged revitalised after the interval, Benjamin Corgnet thumping the ball into the side netting after Yohan Mollo's effort was blocked, then substitute Melvut Erding forcing PSG keeper Salvatore Sirigu into producing a deft save.
PSG, who lost Yohan Cabaye to injury, the former Newcastle midfielder replaced by Marco Verrati, eventually managed to reassert themselves to hold out for the win and move closer to sealing the championship.
Zlatan's two goals take him past Carlos Bianchi's PSG record of 39 goals, which he netted in the 77-78 season.