Quadruple winner of the competition between 2018 and 2021, City never recovered from a completely failed first period when Erling Haaland, Kevin de Bruyne, Riyad Mahrez, Bernardo Silva or Rodri were on the bench.
With a team that included Kyle Walker, Aymeric Laporte, Ilkay Gündogan, Phil Foden and Jack Grealish, as well as the Argentine world champion Julian Alvarez at the forefront, Pep Guardiola's men had serious arguments.
But, reinvigorated by their first victory at Crystal Palace (2-1) in the FA Cup this weekend, the first against a Premier League team since the arrival of Nathan Jones on the bench at the beginning of November, the Saints have grabbed the reigning English champion by the throat.
It was the young French hopeful Sekou Mara (20) who opened the scoring with an uncontrolled recovery (1-0, 23rd) for his first goal in the Southampton jersey, before Moussa Djenepo took advantage of a placement fault of Stefan Ortega, advanced on his six-meter line, to easily lob the German goalkeeper from nearly 30 meters (2-0, 28th).
Even more surprisingly, the entries of De Bruyne (46th), Haaland (56th), or Rodri (63rd) did not change anything for City which did not frame a single shot of the match, out of seven attempts.
In the other quarter-final of the evening, the two poorly ranked Nottingham Forest (15th) and Wolverhampton (19th) needed penalties to decide after a draw (1-1) where the Mexican Raul Jimenez had answered (64th) at the opening of the score of Willy Boly (18th).
In this game, Nottingham was the least clumsy with only one failed attempt against two for Wolves.
In the semi-finals, Nottingham will face Manchester United, who on Tuesday got rid of Charlton, resident of the 3rd division (3-0).
The first leg will take place at the City Ground the week of January 23 and the return at Old Trafford a week later.
Southampton will receive at Saint-Mary's Stadium Newcastle, winner of Leicester (2-0), on Tuesday, in the first leg and will go to Saint James' Park on the return.
© 2023 AFP