Pep Guardiola reacts as Man City are dumped out of the Carabao Cup

First-half goals from Saints pair Sekou Mara and Moussa Djenepo stunned the eight-time winners on an extraordinary evening at St Mary’s.

Pep Guardiola began with Haaland and De Bruyne on the bench for the second successive game ahead of Saturday’s Manchester derby at Old Trafford.

But, unlike on Sunday when the influential pair were not required in a thumping 4-0 FA Cup victory over Chelsea, the decision backfired as they were unable to prevent City suffering elimination after coming off the bench in the second period.

"The better team won. We didn't play good, we didn't play well in the beginning,” said Guardiola.

"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."

Battling underdogs Southampton fully merited victory and will face Newcastle in their first League Cup semi-final since going on to finish runners-up in 2017.

A remarkable result on the south coast was Saints’ first home success over Premier League opposition since they beat Chelsea in August and only a sixth since the start of 2022.

Southampton overcame League One clubs Cambridge, Sheffield Wednesday and Lincoln to reach this stage but the vast number of empty seats suggested many home fans did not envisage further progression.

Yet Nathan Jones’ bottom-of-the-table side set aside their dire league campaign and dismal home form as an aggressive start prevented City slipping into their formidable rhythm and paved the way for a monumental upset.

Lyanco epitomised Saints’ steel with his robust early treatment of Jack Grealish and he was instrumental in the 23rd-minute opener.

After cutting out Sergio Gomez’s pass to Grealish, the Brazilian defender raced forward and delivered a low cross which Mara emphatically swept past Stefan Ortega to claim his first goal for the club.

City’s sold-out away end were briefly silenced by the surprise breakthrough and they had serious cause for concern only five minutes later as Djenepo doubled the lead.

The Mali international collected the ball just inside opposition territory and accelerated towards goal before unleashing a speculative curling effort from 30 yards which sailed over the head of stranded goalkeeper Ortega.

City’s best chance of an alarming first half fell to captain Ilkay Gundogan, who fired wide inside six minutes, and Guardiola responded by bringing on De Bruyne, Nathan Ake and Manuel Akanji for the second period.

De Bruyne almost made an immediate impact but, after his through ball cut open Saints’ defence, Julian Alvarez flashed wide.

The ineffectual Grealish then escaped punishment for a needless, off-the-ball barge on Djenepo before being promptly replaced by Haaland.

Top scorer Haaland, seeking to add to his 27 goals this term, hooked over before Che Adams had an effort ruled out for offside at the other end.

Southampton have kept only one league clean sheet all season but protected their two-goal lead with relative ease.

World Cup winner Alvarez threatened to halve the deficit with 12 minutes to go, while Haaland went close with a flicked header on an evening to forget for the Premier League champions.