Andre Villas-Boas' Marseille opened up a six-point lead over third-placed Rennes, who lost 1-0 at Lille on Tuesday, by bouncing back from successive goalless stalemates against Bordeaux and Angers.
The match was delayed by 15 minutes after clashes between the two sets of fans outside the Stade Geoffroy-Guichard.
According to firefighters and the Saint-Etienne prosecutors' office, there were no injuries or arrests, but sources said that the game was played without visiting supporters -- believed to number around 400 -- who left under police escort.
Payet gave Marseille a seventh-minute lead with a magnificent individual goal, shaping to cross before cutting onto his left foot and hammering the ball past bewildered home goalkeeper Stephane Ruffier from what seemed an impossible angle.
The former West Ham United star has scored 10 goals in all competitions this season.
Saint-Etienne rarely threatened, although Marseille goalkeeper Steve Mandanda had to be alert to keep out Lois Diony's effort shortly before half-time.
The away side made the points safe in the 85th minute, as Nemanja Radonjic drilled a fine left-footed shot into the bottom corner.
Earlier on Wednesday, Lyon failed to close the gap to the top three as they were held to a goalless draw at home by lowly Amiens.
Rudi Garcia's side sit sixth in the table, seven points adrift of Rennes, who occupy the third and final Champions League qualification spot.
Rayan Cherki, 16, came off the bench but was denied a winner when his effort struck the post.
"Too many players have been below their normal level," said coach Garcia. "We gave our best and it wasn't much."
Elsewhere, bottom club Toulouse were cut further adrift with a 1-0 loss to Strasbourg, while Montpellier moved into fifth despite a 1-1 home draw with Metz.
On Tuesday, PSG edged to a 2-1 victory at Nantes to strengthen their position at the top of the table.