Club record goalscorer Cavani netted a superb opener inside nine minutes to seemingly set the tone for PSG to soar to victory, yet the champion appeared to feel the absence of the world's two most expensive players as its momentum waned.
Thomas Tuchel's men were still able to hold on for a 14th consecutive victory to start the Ligue 1 season, but the story may well be different when Liverpool arrives in Paris for a make-or-break Champions League meeting.
PSG will hope to see Neymar and Mbappe on the pitch rather than in the stands for that match, having underwhelmed against a modest domestic opponent.
With the focus on his absent team-mates, Cavani did not take long to provide a reminder of his talents. The forward claimed a loose ball in the area with his back to goal, turned brilliantly past his marker and thumped a volley into the net.
However, PSG's suffocating possession initially led to few further openings and, after Cavani had a second goal disallowed, Toulouse threatened with a couple of speculative efforts before the break.
There was more urgency to the hosts' play at the start of the second half and Thomas Meunier headed over, but that just about proved to be the extent of their attacking ambition.
Christopher Jullien blazed over at the other end when he should have equalised, before Presnel Kimpembe crucially intervened on the goal-line to protect the points in a nervy finish.