The victory at the Parc des Princes in Paris without injured talisman Zlatan Ibrahimovic was PSG's 11th in a row in all competitions and they have not conceded a goal in the league this year.
Ibrahimovic missed the game after suffering a muscle injury during the French champions' 3-1 home win over Chelsea in the Champions League quarter-final first leg on Wednesday.
They have 79 points with six matches left, to Monaco's 63 with seven to play including Sunday's home game against Nantes. Lille, in third on 57, play at Toulouse later on Saturday.
Cavani, spearheading a largely reserve PSG side, put them ahead two minutes before the interval with his 15th league goal of the season, tapping the ball home from Gregory van der Wiel's cross.
The home side increased the lead three minutes into the second half when the unfortunate Mandi helped a header by Brazilian Lucas into the net.
The Reims right back sealed the result with another own goal one minute from time as PSG sealed an easy win with several first-team regulars rested for the Champions League visit to Stamford Bridge next week.
In the day's later games, Lille kept up the pressure on second-placed Monaco with a 2-1 win over Toulouse and Montpellier toppled Guingamp by the same scoreline. Bastia's clash with Sochaux finished 2-2, as did Bordeaux's game with Rennes.
Lorient and Evian Thonon Gaillard played out a 1-1 draw.
- Sports & Recreation
- Zlatan Ibrahimovic