Manchester - English champions Manchester City face the prospect of a third Champions League group-phase exit in four years after a disastrous 2-1 loss at home to CSKA Moscow on Wednesday.
CSKA claimed a first win on English soil at the sixth attempt after Seydou Doumbia scored either side of a free-kick by Yaya Toure, who was sent off in the second half at the Etihad Stadium along with team-mate Fernandinho.
CSKA's Pontus Wernbloom avoided a second yellow card in an apparent case of mistaken identity, but City manager Manuel Pellegrini said referee Tasos Sidiropoulos was not to blame for his side's dismal performance.
"I don't think the sendings-off decided the match. It was in the first half when we weren't ourselves," he told Sky Sports.
"It is a crisis of confidence and we must find out why by talking to the players every day and working together."
Fernandinho, a half-time substitute, was dismissed for two bookable offences and key midfielder Toure was red-carded for pushing Roman Eremenko in the face, leaving the home side with only nine men.
Both players will miss City's next game, at home to Bayern Munich on November 25, when if Pellegrini's side fail to win and there is a victor in the other Group E game between CSKA and Roma, they will be out.
"We had chances in the first half and the second half, and we're happy that our plan worked," said CSKA coach Leonid Slutsky.
"The fact there were two red cards awarded makes us feel we made their players very nervous."
On a cold night in Manchester, City's fans booed the Champions League anthem in protest after away supporters were prevented from watching the 2-2 draw between the teams in the reverse fixture two weeks ago.
That game was played behind closed doors due to a punishment imposed on CSKA for racist chanting by their supporters.
City's fans reacted angrily when they realised that a small band of CSKA supporters had made their way inside the Etihad despite being banned, chanting for their removal until police escorted the interlopers out.
City made the worst possible start when Doumbia, who retired from international football earlier this year, escaped the attentions of former Ivory Coast team-mate Toure to head in Bebras Natcho's right-wing free-kick in the second minute.
Toure allowed his man to slip away from him too easily, but the hulking midfielder atoned six minutes later when he swept a glorious 25-yard free-kick into the top-left corner after a foul on Stevan Jovetic.
Visiting goalkeeper Igor Akinfeev twice saved from Sergio Aguero and once from Martin Demichelis as City attempted to assert control, but sloppiness at the back meant that the home side continued to look vulnerable.
Doumbia gave them a scare when he ran onto Alan Dzagoev's sumptuous through-ball before shooting narrowly wide, and City did not heed the warning.
Eleven minutes before half-time, Gael Clichy played a blind, panicky clearance straight to Natcho, and the Israeli freed Doumbia to roll his second goal of the night past the exposed Joe Hart.
Pellegrini had kept faith with the team that beat Manchester United 1-0 on Sunday, but he shook things up at half-time, introducing Samir Nasri and Fernandinho for Jovetic and Jesus Navas.
City began to force CSKA back, James Milner curling in a cross that narrowly eluded Aguero and then forcing Akinfeev to save with his legs.
But with 20 minutes to play they lost Fernandinho, who was shown a second yellow card for blocking off Ahmed Musa, only eight minutes after he had been booked for fouling Dzagoev.
Sidiropoulos angered City by booking Sergei Ignashevich after Wernbloom, who had already been booked, held back Aguero, but Toure could have no complaints over his straight red card for a petulant shove to the face of Eremenko.
To add insult to injury, Aguero was booked for diving and also saw a strong penalty appeal turned down in stoppage time.