Jude Bellingham scored the winner in stoppage time as Real Madrid twice came from behind to inflict more misery on Manchester City, with a 3-2 Champions League playoff, first-leg win at the Etihad.
Erling Haaland twice put City in front with his first goals in five games against Madrid on Tuesday.
But the holders hit back through Kylian Mbappe and Brahim Diaz before Bellingham stroked home in the 92nd minute on his return to England.
City now have a monumental task ahead to progress to the last 16, when the sides meet again in the Spanish capital on February 19.
The clubs were meeting for the fourth consecutive season in the Champions League, with the winners in each of the previous three years going on to lift the trophy.
If that familiarity did not breed enough contempt, Madrid’s decision to boycott City midfielder Rodri’s crowning as the Ballon d’Or winner last year added extra animosity.
The midfielder was rewarded for his role in Spain’s Euro 2024 triumph and a fourth consecutive Premier League title.
However, the Spanish giants took umbrage at Vinicius Junior being overlooked for the prize and pulled out all of their representatives from the ceremony in October.
A huge banner before kickoff showed Rodri with the Ballon d’Or trophy alongside the lyric “Stop crying your heart out” from the City-supporting band Oasis.
Rodri’s absence since September with a season-ending knee injury has played a major role in City’s decline this season as the English champions sit 15 points off the pace in the Premier League.
In recent years, Madrid have been pegged back on the ropes at the Etihad, twice conceding four times in three visits.
This time, the visitors had a series of early chances to sow more doubt in City’s minds.
Vinicius’s every touch was booed, and the home fans were delighted when he had a penalty ruled out for straying offside before he was wiped out by Ederson.
The City goalkeeper then made a vital save from Mbappe, and Nathan Ake deflected Ferland Mendy’s shot wide with the goal gaping.
Pep Guardiola’s men hit the visitors with a sucker punch on 19 minutes, thanks to a brilliant team goal.
Jack Grealish’s dinked cross was chested down by Josko Gvardiol into Haaland’s path, who stayed millimetres onside before stroking home his 26th goal of the season.
Real came roaring back as Vinicius’s effort came back off the bar.
City also hit the woodwork through Manuel Akanji, and Thibaut Courtois was forced into a spectacular save from Phil Foden.
Haaland remained a constant threat to Madrid’s injury-ravaged defence.
Ancelotti was forced to name midfielders Federico Valverde and Aurelien Tchouameni in his backline alongside the inexperienced Raul Asencio.
Haaland’s deflected effort that came back off the crossbar seconds into the second half proved a turning point as Madrid again took control.
Bellingham headed wide and Ederson denied Mbappe as the pressure built before it finally told on the hour mark.
Mbappe’s finish was far from his cleanest but his mishit from Dani Ceballos’s cross deceived Ederson and looped into the net.
Madrid smelled blood and went for the kill. Valverde drilled inches wide before Bellingham should have scored when he shot low into the legs of Ederson.
But it was City who got the third goal when Foden was brought down by Ceballos as he weaved a way into the penalty area and French referee Clement Turpin pointed to the spot.
Haaland sent Courtois the wrong way for his 49th goal in 48 Champions League appearances.
Yet, by full-time, the Norwegian was a disconsolate figure as City’s poor campaign took another turn for the worse.
Diaz had only been on the pitch a matter of seconds when he fired in against his old club after Ederson parried Vinicius’s effort into his path.
Moments later, the Brazilian goalkeeper was caught in no-man’s land as Vinicius ran through, and even as his attempt was heading wide, Bellingham stole in for a simple finish.
