A Paris Saint-Germain side missing the injured Lionel Messi and Kylian Mbappe and hit by a stomach bug warmed up for their Champions League showdown against Bayern Munich by falling to a 3-1 defeat at Monaco in Ligue 1 on Saturday.
All the goals came in the first half at the Stade Louis II, with Aleksandr Golovin putting Monaco ahead inside four minutes and Wissam Ben Yedder doubling the home side's lead.
PSG remain top of the table, although their lead has been reduced to five points over Marseille, who won 2-0 at Clermont.
Monaco are now up to third, seven points behind the leaders, but seeing the gap to their rivals reduced is the least of PSG's worries right now, after they went down to their second defeat in four days.
Also beaten by Marseille in the last 16 of the French Cup in midweek, Christophe Galtier's team have now lost three times in seven league outings in 2023.
PSG will be without Mbappe, their top scorer, due to a thigh injury for the Champions League last-16 first leg with Bayern at the Parc des Princes on Tuesday.
Galtier must also hope that Messi recovers in time from the hamstring complaint that prevented him from travelling to the principality.
PSG were also without playmaker Marco Verratti, fellow midfielder Renato Sanches and defender Nordi Mukiele due to injury before it emerged that several members of the squad were laid low by a stomach bug on the morning of the game.
"We are having to do what we can with the players we have available just now. It is bizarre to say that when you're PSG but that is the situation," said Galtier.
Experienced players such as Sergio Ramos and Achraf Hakimi only appeared in the second half before Presnel Kimpembe made his first appearance since prior to the World Cup following injury.
PSG were already 3-1 down by the time any of them came on and would have suffered a heavier defeat had goalkeeper Gianluigi Donnarumma not been in inspired form.
After the game Kimpembe used a megaphone to apologise to PSG's travelling supporters.
"If I were not worried just now there would be something seriously wrong," Galtier added.
"We have a packed schedule and a weakened squad but we are worried.
"I understand the fans' anger. It is warranted, but we need to all stick together in these difficult moments."
Already beaten by Lens and Rennes in Ligue 1 since the turn of the year, the capital side fell behind when Ben Yedder helped set up Russian international Golovin to score from close range.
El Chadaille Bitshiabu, the 17-year-old centre-back, was then dispossessed on the edge of his own area by Krepin Diatta, allowing Ben Yedder to fire in and make it 2-0 in the 18th minute.
Donnarumma saved well from Ruben Aguilar before the visitors pulled one back as Juan Bernat's low ball across the face of goal was turned in by Zaire-Emery.
Yet Donnarumma had to save again from Golovin and then France striker Ben Yedder finished with aplomb to restore Monaco's two-goal lead right on half-time.
- Crowd trouble -
PSG, with Neymar unable to make an impact, rarely threatened in the second half and again needed their Italy goalkeeper to intervene on several occasions, including making a fine stop to deny Takumi Minamino right at the end.
Marseille's game at Clermont did not kick off until almost 10:00 pm, nearly 50 minutes later than planned, after incidents outside the stadium prompted security forces to use tear gas.
Players stayed inside the dressing rooms while supporters were pictured covering their faces as the tear gas drifted across the Stade Gabriel-Montpied.
The local authority told AFP around 100 ticketless fans tried to force their way into the venue and were pushed back by the security forces, before vandalising fencing to enter the car park for visitors.
Alexis Sanchez scored both goals for Marseille, netting a penalty just before half-time and then heading in a late second.