The Premier League champions were at their sumptuous best this afternoon, opening up a 3-0 lead inside the opening 18 minutes thanks to an own goal from Wesley Hoedt, and strikes from Man City legends Sergio Aguero and David Silva.
Aguero's seventh league goal of the season took him level with Pierre-Emerick Aubameyang and Eden Hazard in the Golden Boot race.
Both of the England forward's goals were assisted by Aguero, as the Argentine first crossed for Sterling to stroke in, before a slide-rule pass enabled the 23-year-old to finish emphatically. He is stable and is focused on what he has to do to become a better player.
"It was an incredible performance but still with the young guys like him and Leroy [Sane] I would feel he can improve. We can not forget that".
"Last year was hard for me for many things".
Then came something of a drought as 12 minutes passed before Danny Ings converted a penalty to bring some respectability to the score for Southampton but Raheem Sterling restored City's three-goal margin right on half-time. "I am not asking Sergio to be Gabriel (Jesus) or Kyle Walker but I am asking for the best Sergio...to be aggressive, with and without the ball".
Marcus Rashford fires Manchester United to injury-time victory over Bournemouth
Maybe Mourinho could take something from that change as United prepare to face Juventus and Manchester City in this crucial week. United have kept just one clean sheet in 11 Premier League games this season. "But I think the impact was Ander Herrera ".
Morata has now scored four in his last four Premier League games after just two goals in his previous 20 domestic matches, and his return to form could be the final ingredient Sarri's side need to mount a serious title challenge.
Southampton are in 16th place, two places above the relegation zone with a solitary win this campaign and manager Hughes was left to rue the disastrous start to the game. Now you have the feeling [he thinks], "Where is the goal and go there".
Sane's goal was his third of the season and his second in three Premier League matches, but he admitted there was an element of luck involved.
"It is hard when you are down", Hughes added.
"He is more mature now than he was when we first met at the club".
"Six-one is not a result we take any pride in but the fact we were trying to create chances when the game was gone shows the character was good".