Paris Saint-Germain's 10 men slipped up at the Ligue 1 summit once again after they suffered a 3-1 loss against a worthy Lorient on Sunday.
Achraf Hakimi's 20th-minute dismissal for a second yellow card followed Enzo Le Fee's surprise opener for the visitors at Parc des Princes.
Although Kylian Mbappe brought Christophe Galtier's side back on equal terms with a controversial finish, goals from Darlin Yongwa and Bamba Dieng handed the hosts another defeat.
It is their third in sixth league matches, although PSG retain a healthy gap to second-placed Marseille, eight points back with a single game in hand.
The signs of a potential PSG implosion were there inside the opening exchanges when Hakimi clattered through Romain Faivre with his studs.
It went from bad to worse for the home side when Le Fee smashed in from six yards following a cut-back, before Hakimi got his marching orders after he lunged in on Yongwa's foot.
Mbappe restored parity with a moment of bizarre opportunity after goalkeeper Yvon Mvogo mistakenly thought he had a free-kick and dropped the ball in his box, allowing the striker to pounce on an open net.
But Lorient would not be kept level for long, and when a defensive block inside the PSG box went awry, Yongwa was there to pounce and claim back the lead.
Despite the man disadvantage, PSG pushed hard for another equaliser after the break, with Sergio Ramos inching a header over before the hour mark.
Lorient picked them off on the counter, however. After Dieng saw a tap-in chalked off for offside late on, he belatedly got his goal after seizing on a long ball for a breakaway goal.
What does it mean? PSG slip up again
After losses either side of the international break stemmed their momentum, three wins on the trot had got PSG back to winning ways.
But this loss might leave the door slightly ajar for Marseille, who stand to profit if the champions continue to slip up.
Hakimi absence leads to leaks
PSG's defence has not always been the most steadfast, but they have generally been resolute at home.
That changed this weekend. For the first time in the QSI era (since 2011-12), they lost a home game in Ligue 1 conceding at least three goals.
Bamba from the bench
Dieng would not be denied late on, having seen a goal disallowed for offside seconds before finding the net again.
Even with that first effort struck off, the substitute had the joint-most shots (three) of any Lorient player.
What's next?
PSG head to Troyes next Sunday, while Lorient host Brest.
