Second-string PSG beaten by Strasbourg before Arsenal return leg
A Lucas Hernandez own goal put Strasbourg ahead on 20 minutes and Felix Lemarechal doubled the home side's lead in first-half stoppage time in Alsace, although Bradley Barcola pulled one back for PSG just after the break.
Liam Rosenior's in-form Strasbourg are now unbeaten in 12 games going back to early February and this victory lifts them up to fourth in the table ahead of the rest of the weekend's fixtures.
PSG have already wrapped up a fourth consecutive Ligue 1 title and saw their unbeaten record domestically this season come to an end last weekend.
Coach Luis Enrique therefore rested all of those who started the 1-0 win away to Arsenal in the first leg of their Champions League semi-final on Tuesday, with the exception of Portuguese midfielder Joao Neves.
Ousmane Dembele, who scored the winning goal against the Gunners, was missing altogether after coming off hurt in the second half of that game.
It remains to be seen if Dembele, PSG's leading scorer with 33 goals this season in all competitions, will be fit for the return leg in Paris on Wednesday.
Luis Enrique gave a top-flight debut at the Stade de la Meinau to 17-year-old centre-back Axel Tape and just a third start in Ligue 1 to winger Ibrahim Mbaye, also just 17.
Strasbourg took advantage of their visitors' inexperience as they went ahead on 20 minutes when Mamadou Sarr helped on a corner and the ball went into the net off the unfortunate Hernandez.
Goncalo Ramos had a couple of chances for the visitors in the first half but Strasbourg scored again just before the interval.
Habib Diarra advanced down the right before teeing up Lemarechal to score with a fine first-time strike from the edge of the area, high into the far corner.
Hernandez and Lee Kang-in, who had been struggling with a knock, were both replaced at the restart as another teenager, 18-year-old defender Noham Kamara, came on for his Ligue 1 bow.
PSG got a goal back less than a minute into the second half as Barcola ran over half the length of the field before stabbing in his 19th goal of the campaign in all competitions.
However, Strasbourg held on for the rest of the game, including through eight minutes of stoppage time.
They are now just a point behind second-placed Marseille, who go to Lille on Sunday, and sit only goal difference behind third-placed Nice, 1-0 winners against Reims on Friday.
If Strasbourg can hold their place in the top four, they will qualify for next season's Champions League, having not graced Europe's elite club competition since 1979/80.
However Lille, Monaco and Lyon are all within three points ahead of their fixtures this weekend, with the principality side away to Saint-Etienne later on Saturday.