The Blues were well below par on a disappointing night at St Mary’s with the home side good value for their victory.
City looked hesitant from the word go, with Southampton starting confidently.
A little like the opening period against Chelsea at Stamford Bridge, the Blues had trouble imposing their game on the side that sits bottom of the Premier League, allowing the hosts’ belief to grow as the minutes passed.
And the laboured start from Pep Guardiola’s men finally proved costly when Southampton struck twice in the space of five minutes midway through the opening period.
A number of loose passes preceded a break down the right by Southampton that ended with Sékou Mara meeting a low cross with a crisp drive past Stefan Ortega.
And five minutes later Moussa Djenepo burst forward, spotted Ortega off his line, and sent a 25-yard chip sailing over his head into the net.
It was rapidly turning into our most underwhelming first 45 minutes of the season against a side who often seem to find that something extra when City come to town.
Just as he did in the Chelsea clash mentioned earlier, the boss decided he’d seen enough and rang the changes at the break.
Before the hour, Erling Haaland was introduced as City looked to find a way back into a tie few predicted would transpire the way it was doing.
But the home side refused to buckle, challenging for every ball as though their lives depended on it, aggressively defending in numbers and City just couldn’t get going.
City were better in the second period, but the damage had been done in the first half and this season’s Carabao Cup adventure is over.
What it means….
City will turn focus to the three competitions we remain in – the FA Cup, Champions League and, of course, defending the Premier League crown.
City make the short trip across the city to face United in the Manchester derby at Old Trafford.
The Reds have won their last eight games and are just four points behind the Blues.
The game kicks off at 12:30pm on Saturday lunchtime.
"The better team won. We didn't play good, we didn't play well in the beginning. There are many games you can start not good and overcome and we didn't do it.
"When you are not prepared to play this game you arrive one inch late and don't score a goal. When you are prepared, you score the goal.
"Today was a bad night, the opponent was better so we have to congratulate them. To win games you have to deserve it and tonight we didn't deserve it.
"We struggled to make the build up. When we don't make the passes good then we struggle.
"We had a bad night, we were not ready to play a game away in England.
"From the way we played they didn't look ready. It was not good.
"We will prepare as best as possible for United and do our best."
"We were very disappointing. The result, but also the performance. It’s definitely not what we wanted.
"We had hopes of going through in the Carabao Cup, but with that performance there was no chance. It was not enough from us.
"We were not aggressive enough; not winning duels, giving them opportunities to play.
"With the ball we made a lot of mistakes, missed a lot of passes, gave them the ball too easily and that resulted in the two goals.
"Today we were not good enough to create chances, not good enough to score a goal. The mix of the performance from all the team gives this result."
Saints: Bazunu, Caleta-Car, Lyanco, Salisu, Lavia (Elyounoussi 62), Djenepo (Perraud 57), Ward-Prowse, Diallo, Walker-Peters, Mara (Adams 62), Armstrong (Orsic 83)
Unused subs: Aribo, Caballero, Edozie, Morgan, Finnigan
News about Saints v Man City
Southampton 1-4 City: Pitcam highlights
Watch our comprehensive Premier League victory on the road at Southampton from a unique perspective. Watch more
Pitcam highlights: Southampton 2-0 City
Watch City’s Carabao Cup quarter-final meeting with Southampton from a unique angle. Watch more
Saints 2-0 City: Extended highlights
Extended action from St Mary's... Watch more
Saints 2-0 City: Short highlights
Brief action from St Mary's... Watch more
Full-match replay: Southampton v City
Watch the full 90 minutes of City's Carabao Cup quarter-final clash with Southampton at St Mary’s Stadium on CITY+ and Recast. Watch more
Guardiola: We weren't ready
Pep Guardiola says that his team weren't ready for the stern test Southampton presented. Watch more
'We had a bad night' says Pep after Carabao Cup exit
Pep Guardiola said that City didn’t deserve to make it into the semi-finals of the Carabao Cup following the 2-0 defeat to Southampton. Read more