Paris St Germain's Ligue 1 title charge suffered a surprise blow as they slumped to defeat away to the 10 men of relegation-battling Reims.
Zlatan Ibrahimovic had a goal controversially disallowed early in the second half, and Reims then had Christopher Glombard sent off for a second bookable offence before the hour mark.
But Reims still ran out winners as Grzegorz Krychowiak scored the only goal in the 64th minute.
The result means that Lyon can move level on points with PSG by beating Brest away from home tomorrow.
David Beckham returned to the bench for PSG, who squandered a string of chances on their way to a second defeat in three.
The hosts made a positive start but it was PSG who were the first to find the target in the 15th minute, with Ibrahimovic bringing a save from Kossi Agassa after being picked out by Blaise Matuidi.
At the other end Antoine Devaux brought a solid save from Salvatore Sirigu with a stinging 25-yard drive pushed away by the Italian's outstretched hand.
Reims' Brazilian Diego shaved the right post just after the half-hour mark before Ezequiel Lavezzi had the best chance of an opener at the other end, only to fire wide with only Agassi to beat.
Agassi was called into action once again soon after - this time the keeping out Ibrahimovic's long-range free-kick - before Reims' Gaetan Courtet headed wide from a promising position.
PSG thought they had the lead early in the second half when Ibrahimovic got in behind the Reims defence and finished confidently but the Swede's 23rd goal of the season was chalked off for a questionable offside.
Reims' chances of getting anything from the game looked to have taken a huge dent just before the hour when Glombard brought down Javier Pastore and was shown a second yellow card.
But despite the numerical disadvantage it was the hosts who took the lead in the 64th minute.
Mohamed Fofana knocked a Diego corner into the path of Krychowiak and, having escaped the attentions of Alex, the Polish midfielder finished from a tight angle.
PSG threw on Beckham in an effort to change the game and Lavezzi should have done better with a curling shot moments after the former England captain's entrance but his effort finished well wide.
The Parisians continued to dominate with the man advantage and Lavezzi was guilty of missing the target once more - this time the Argentinian snapped at a Sylvain Armand cutback and failed to test Agassa.
In a rare venture forward, Reims' Fortes nearly scored a contender for goal of the season but, after beating Mamadou Sakho and Alex, the Ivorian's shot from the edge of the area was well saved by Sirigu and the 10 men of Reims held out for a famous victory.