Terem Moffi upstaged Kylian Mbappe with two goals and an assist to help Nice win 3-2 at Paris Saint-Germain in the French league, handing the defending champions their first defeat under new coach Luis Enrique.
It was a worrying loss for the home fans despite Mbappe also scoring twice, with PSG's opening game of the Champions League on Tuesday against Borussia Dortmund.
PSG's lingering defensive frailties were again exposed, this time by the clinical finishing of the Nigeria striker. Moffi's pace and wide runs off the ball were ideally suited to the excellent counterattacking of unbeaten Nice.
This was a costly defeat for PSG, who are one point behind second-place Nice and two behind leaders Monaco, who play at Lorient on Sunday.
Moffi set up Nice's other goal with a fine run down the left and a pinpoint cross to striker Gaetan Laborde at the far post.
Moffi put Nice ahead when he profited from a scramble in the penalty area to clip a slightly deflected shot inside the near post past goalkeeper Gianluigi Donnarumma in the 21st minute.
Mbappé equalised eight minutes later when he whipped in a quick shot from 20 metres past former PSG 'keeper Marcin Bułka.
But Moffi then set up Laborde for a sliding finish in the 53rd before getting the goal of the night in the 68th.
Controlling a pass in midfield with his back to goal, he flicked the ball astutely to Laborde down the right and collected his return pass before advancing across the area to plant a low shot past Donnarumma into the bottom left corner.
His celebration, where he removed his jersey and waved it over his head, earned him a yellow card and also annoyed Mbappé, who exchanged words with him at the halfway line.
Forward Randal Kolo Muani was already on as a substitute and he set up Mbappé's close-range finish in the 87th.
Kolo Muani became the third most expensive signing in PSG's history when he joined from Eintracht Frankfurt for 95 million euros ($A158 million).
Only Neymar and Mbappé have cost more.