Paris Saint-Germain suffered their first home league defeat since May 2018 as goals from Hassane Kamara and Boulaye Dia gave Reims a shock 2-0 victory at the Parc des Princes.
The Ligue 1 champions, deprived of a host of key players, were well below their best and a spirited Reims side took advantage.
Kamara powerfully headed home in the 29th minute and, even though PSG piled on the pressure in the second half, the visitors' defence stood firm.
Dia added a second in the fourth minute of injury time with a spectacular bicycle kick.
44 - Paris have failed to score for the first time in 44 Ligue 1 games, it was the longest such-run in the history of the French top-flight. Down. pic.twitter.com/pJI3bIK2i7— OptaJean (@OptaJean) September 25, 2019
PSG were without the attacking qualities of Julian Draxler, Edinson Cavani, Kylian Mbappe and the on-loan Mauro Icardi – all absent through injury – while Marco Verratti was suspended.
It meant much of PSG's impetus in the final third fell to Neymar, whose knack of scoring late goals secured back-to-back 1-0 wins against Strasbourg and Lyon in Ligue 1.
However, Reims packed the midfield and swarmed around the Brazilian whenever he received the ball, stifling Neymar's impact, although he did go close with a free-kick that curled narrowly over.
The visitors took a surprise lead just before the half-hour mark when Kamara netted his first top-flight goal.
PSG goalkeeper Keylor Navas almost kept out Kamara's header from Marshall Munetsi's cross with a spectacular one-handed diving save, but the Reims midfielder's effort had too much power and went in off the post.
Thomas Tuchel's side dropped points in an away defeat to Rennes last month, and they only threatened sporadically in their quest to avoid a second league loss of the campaign.
PSG had not been beaten at home in the league for 22 games since suffering a 2-0 reverse at the hands of Rennes, but they went down by the same margin when Dia got on the end of Thomas Foket's cross and volleyed home in stunning fashion.
What does it mean? No early breathing room for PSG
Shorn of many of their stars, PSG were unable to break down a dogged Reims side and now only lead Ligue 1 on goal difference ahead of second-placed Angers, who won 2-0 at Toulouse.
Kamara caps brilliant performance
It was a night to remember for Kamara. He opened the scoring and went close to doubling his tally. Disciplined in central midfield, he was pivotal to Reims' third league win of the season.
Choupo-Moting fails to fire
PSG needed Eric Maxim Choupo-Moting to provide a goalscoring threat but the former Stoke City man struggled to make an impact. He then joined PSG's injury list when he limped off just before the break.
PSG have an away fixture at mid-table Bordeaux on Saturday while Reims are in action on the same day when they host Dijon.