The Saints took an unlikely lead in the 13th minute through James Ward-Prowse, who tapped in after Ederson saved from Stuart Armstrong.
The hosts looked for an instant response but found themselves up against a well-organised Southampton backline.
We dominated possession and finally levelled the scores with 20 minutes remaining through Aguero, who calmly stroked the ball through McCarthy’s legs following an accurate cutback from Walker.
City had a spring in their step and almost found the net again with ten minutes left, but Bernardo’s powerful drive was tipped over by the stretching McCarthy.
The Etihad erupted as we finally found a deserved winner in the 87th minute, as Walker finished brilliantly from just inside the box.
Here are the best pictures from the hard-fought victory...