A depleted Paris St-Germain side began their Ligue 1 campaign with a surprise loss against newly promoted Lens.
The match was in doubt after Champions League finalists PSG had seven players, including star striker Kylian Mbappe, test positive for coronavirus.
Lens took full advantage on their return to the top flight as Ignatius Ganago punished goalkeeper Marcin Bulka's error to net the winning goal.
The match was played in front of 5,000 fans at Lens' Stade Bollaert-Delelis.
PSG have won seven of the past eight top-flight titles including last season when the campaign was ended early because of the coronavirus pandemic. Thomas Tuchel's side finished 12 points clear at the top of the table.
Brazil forward Neymar, compatriot Marquinhos and Argentina internationals Angel di Maria and Mauro Icardi were all missing for the visitors.
It proved costly as third-choice goalkeeper Bulka presented the ball straight to Ganago to fire home the only goal of the game in the second half.
PSG host Marseille in the league on Sunday (20:00 BST) and must wait to see if any of the missing players will be available for selection.