Paris Saint-Germain's poor start to 2023 continued as Wissam Ben Yedder scored twice in Monaco's 3-1 win over the Ligue 1 leaders, who sorely missed the injured Lionel Messi and Kylian Mbappe.
Hamstring issues kept Messi and Mbappe out at the Stade Louis II, and with the likes of Sergio Ramos and Achraf Hakimi benched, Christophe Galtier's below-strength team were all at sea.
Aleksandr Golovin struck early for Monaco and Ben Yedder doubled up before half-time, punishing an error from 17-year-old El Chadaille Bitshiabu for his first goal.
Sixteen-year-old Warren Zaire-Emery briefly put PSG back in contention before Ben Yedder's second, but PSG's defensive shortcomings ensured they suffered their third league defeat since the turn of the year.
PSG fell behind just four minutes into a calamitous display, Golovin poking home after Youssouf Fofana's powerful run teed up Ben Yedder for a blocked attempt.
Monaco continued to test a nervous PSG backline and punished a mistake from Bitshiabu after 18 minutes, with Ben Yedder drilling beyond Gianluigi Donnarumma after the defender carelessly lost possession.
PSG halved the arrears when Juan Bernat's cut-back found Zaire-Emery for a simple tap-in, but the outstanding Ben Yedder restored Monaco's two-goal lead with a composed one-on-one finish as half-time approached.
Ben Yedder almost brought up his treble with a powerful header after 61 minutes, only for Donnarumma to deny him with a firm one-handed stop.
Donnarumma was then alert to prevent half-time substitute Ramos putting through his own net as PSG escaped further humiliation, but they will need a major improvement ahead of Tuesday's Champions League meeting with Bayern Munich.