Italy worldwide Florenzi, on loan from AS Roma, doubled the tally on 78 minutes with a header before Mbappe struck again five minutes later after being set up by Sarabia.
"We have a bit of bad luck with players", said Tuchel on the eve of the game.
The Ligue 1 clash came just three days after Neymar scored a hat-trick against Peru in World Cup qualifying in Lima to move past Ronaldo and into second for the most goals for Brazil .
"He's the guy who can always make a difference and he did just that".
Leandro Paredes was forced off after he was caught by a Lucas Deaux, who was perhaps fortune to only be booked, so Ander Herrera made an early appearance off the bench.
Landre was sent off moments later for a rash challenge on Rafinha, raking his studs down the side of the ex-Barcelona player's ribs.
"Colin Dagba had a positive (coronavirus test) with the (French) Under-21s".
Florenzi rattled the post twice in the second half, with a volley and header, but the Italy defender eventually gave PSG room to breathe as he nodded in Sarabia's header back across goal.
The Spaniard then caught out the hosts from a quickly-taken free-kick to smack in a fourth through the legs of Reynet two minutes from the end.
Last season, PSG had a 75 per cent win percentage without Neymar in 12 Ligue 1 games, while it was 86.7 per cent when he featured.
Rennes, meanwhile, lost its four previous trips to Dijon but netted midway through the first half when Martin Terrier turned in Hamari Traore's left-wing cross. Midfielder Flavien Tait hit the crossbar late on for Rennes.
Lille or Lens could overtake PSG and Rennes with victory in Sunday's Derby du Nord, the first such fixture in over five years.