Five minutes had gone when Aguero orchestrated an attack on the edge of the Southampton area, David Siva then moving the ball on to the overlapping Sane, whose cross was turned into his own goal by Saints' Wesley Hoedt.
City restored their three-goal advantage before the interval, however, thanks to Sterling's simple finish past McCarthy after Aguero kept the ball in play and squared it to his teammate, though the Englishman required a couple of bites of the cherry after miscuing his initial shot.
It was Sterling who got the game's next goal too on 67 minutes before Leroy Sane put the icing on the cake after the 90th minute to make it six.
The visitors initially improved after the break, with James Ward-Prowse and Ings forcing Ederson into three vital saves between them.
Southampton headed into the match winless in six league matches and without a goal in five of them, and what was always going to be a hard task was made even tougher when conceding six minutes in.
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We made, I think, more mistakes than the refs but I think in this moment it would have been cool if the goal could count. Unai Emery 's side are fourth in the table, but will move to within one point of Liverpool with three points.
Sterling struck again to make it 5-1, drilling into the bottom corner after being slipped in by the unselfish Aguero and Sane completed the rout in stoppage time.
What does it mean?
"You can see we're keeping going with how we play from last season, we enjoy playing together".
Bernardo told CityTV: "I'm feeling well". The England worldwide was absolutely everywhere, no wonder he is reportedly in line for a new five-year contract.
Southampton had the minor consolation of becoming the first team in 630 minutes to score against City but the leaders' form is ominous for the rest of the division. They settled for six goals in the end - the fourth time in 11 Premier League games that they have scored at least five times in a game - and might easily have scored more had the occasion demanded more ruthlessness.
- Sterling scored his 50th goal in all competitions for the club in what was his 153rd game and 126th start.