Penalty shoot-out winners when these sides met in the Coupe de France final last season, the hosts produced another shock result over the top-flight champions thanks to goals either side of half-time at Roazhon Park.
5 - Rennes are the team who have won the most games against Paris in Ligue 1 over the past 10 seasons (5 wins in 19 games). Roazhon. pic.twitter.com/hTCrYEsUru— OptaJean (@OptaJean) August 18, 2019
Edinson Cavani profited from a defensive error to put Neymar-less PSG into the lead, but M'Baye Niang pulled one back a minute before half-time and Romain Del Castillo headed Rennes in front early in the second half.
PSG, who triumphed when these sides met in the Trophee des France two weeks ago, have now lost five of their last six away matches in the league.
Cavani sent a glancing header crashing off the woodwork with 14 minutes on the clock but he was gifted a goal later in the half.
Rennes captain Damien Da Silva played a stray pass across his own six-yard box and Cavani beat goalkeeper Romain Salin to the loose ball for a simple finish.
But the home side levelled things up through their first on-target attempt of the match as Niang controlled Hamari Traore's cross, swivelled and picked out the bottom-left corner a minute before half-time.
The comeback was complete three minutes in to the second period when 16-year-old midfielder Eduardo Camavinga sent in a delightful cross from the right, which Del Castillo guided away from the reach of Alphonse Areola.
16 - Eduardo Camavinga (16 years & 9 months) is the youngest player to deliver an assist in Ligue 1 since Opta analyze the competition (2006/07). Diamond. pic.twitter.com/Xdcpymv20I— OptaJean (@OptaJean) August 18, 2019
Niang was denied by Areola and Jeremy Morel struck a post with his volley as Rennes closed in on a third.
Ultimately it did not arrive, but Thomas Tuchel's men failed to truly test Salin at the other end as Rennes made it two wins from two.
What does it mean? PSG's away form a cause for concern
If PSG's poor away form continues then Ligue 1 may well have a title race this season. Lyon, Nice and indeed Rennes all have six points from six after three matches, leaving the champions playing catch up at this admittedly early stage.
Camavinga proves age is just a number
He may not turn 17 for another three months, but Camavinga is starting to make a name for himself. The floated cross for Del Castillo's winner was right on the money and he also managed a few attempts of his own.
PSG lack ideas
PSG cruised to a 3-0 win over Nimes in their Ligue 1 opener last week – three of their forward players getting on the scoresheet – but they lacked creativity here in the absence of Neymar, who was overlooked despite returning to fitness. Cavani's goal was a gift and they managed just one further shot on target.
PSG welcome Toulouse to the Parc des Princes next Sunday and Rennes travel to Strasbourg on the same day.