Ligue 1: Reims 1 PSG 0
After a first half full of chances at either end, the winning goal was scored by former Bordeaux man Grzegorz Krychowiak, who headed in from a corner. Earlier, the relegation strugglers were down to 10 following Christopher Glombard's red card.
For all of PSG's enterprising efforts, they were distinctly limited up front, being frustrated by a superbly organised defence, as well as their own profligate finishing as Reims celebrated a famous win.
Following on from a week of victories over arch-rivals Marseille, the visitors aimed to continue their recent good form as Zlatan Ibrahimovic and Lucas Moura combined to test Kossi Agassa in the Reims goal early on.
Hubert Fournier's men - who before this weekend had amassed only one win in 19 games in all competitions - started brightly, as Antoine Devaux forced Salvatore Sirigu into a smart save with an angled shot. Team-mate Diego Rigonato then spurned a glorious opportunity, shooting wide despite having options in the box.
Carlo Ancelotti's side were sluggish at best in the opening exchanges but they were still liable for missing a couple of gilt-edged chances.
They should have been 1-0 down in the 35th minute, though, when Anthony Weber's goal-bound shot was blocked, with Sirigu beaten amid lax defending in the PSG box.
Seconds later, they should have been one up. The Ligue 1 leaders' signature counter-attack resulted in Ezequiel Lavezzi going one-on-one with Agassa, but he fluffed his shot completely.
Ibrahimovic was subsequently thwarted by Agassa with his free-kick beaten away by the Togolese international, though Gaetan Courtet wasted two brilliant chances - set up by the active Franck Signorino - Reims went into the interval the dominating team.
The towering Swede would have a goal wrongly chalked off for offside moments into the second half. Springing the offside trap and played onside by Mohamed Fofana, Ibrahimovic produced a fine finish to beat Agassa, before a controversial offside flag scuppered his side's advantage.
PSG's task was made a little easier after the hosts saw Glombard sent off. The midfielder, playing at right-back following Aissa Mandi's suspension, was shown a second yellow for a poor tackle on Matuidi, but that setback only sought to spur on Reims, who took a deserved lead.
From a corner, Fofana headed on towards the far post, allowing Poland international Krychowiak to head in unmarked, as Reims finally came good following a string of chances.
David Beckham then entered the field as a 64th minute substitute replacing Marco Verratti, but the Ligue 1 leaders failed to ignite at the other end, with further chances from Lavezzi, Matuidi and Lucas Moura all being dealt with by a resolute Reims defence as well as an inspired Agassa.
And Reims could have made it 2-0 but Odair Fortes' superb run saw his goalbound shot parried by Sirigu. And despite a late surge in attacking intensity, Fournier's side held on.