Unai Emery's PSG side put the memory of last week's surprise 2-0 defeat at Toulouse firmly behind them by racing into an early lead when Cavani rose to head home Angel di Maria's cross in the third minute.
The Uruguayan doubled the lead on the half-hour mark by helping Layvin Kurzawa's pass into the net with a clever flick of the heel, grabbing his eighth league goal of the season and adding to his double in Wednesday's 3-1 win at Ludogorets in the Champions League.
PSG now have 16 points, with Monaco on 19 after their away win. Nice, who were top before the weekend with 17 points, host Lorient on Sunday.
Monaco were 3-0 up at the break thanks to goals from Thomas Lemar, Valere Germain and Bernardo Silva.
Cheick Doukoure was sent off for the home side on the hour mark for a dangerous lunge and Monaco took full advantage, further tormenting Metz with a penalty from Fabinho, a double from Guido Carrillo and an 89th minute strike from substitute Gabriel Boschilia.
Lille climbed out of the relegation zone by beating Nancy 1-0 and Toulouse lost 1-0 at Caen.
Cavani's double saw him become the top scorer in Ligue 1, moving two goals clear of Lyon forward Alexandre Lacazette and Metz's Mevluet Erdinc.
"Getting the three points was more important than our performance today," Emery told Canal Plus.
"We played with a lot of confidence and played very well."
Saturday's game saw PSG's hardcore 'Ultra' supporters return to the Parc des Princes for the first time since they were banned in 2010 and they were in good voice from start to finish.
Cavani's early headed goal only turned up the volume and PSG's confidence rocketed as they dominated possession and created chances from all over the pitch before the Uruguayan pounced again.
Di Maria had a goal ruled out for offside at the other end as PSG searched for a third, but their two-goal cushion provided by an insatiable Cavani proved more than enough.
(Reporting by Richard Martin; Editing by Clare Fallon/Alan Baldwin)
