A fully fit Kompany would have saved Guardiola and the City fans a whole load of heartache over the past few months, too.
Mousa Dembele and Heung-Min Son both netted within the space of three first-half minutes and Harry Kane, starting for the first time in almost five weeks, later joined Alan Shearer, Ruud van Nistelrooy and Thierry Henry as only the fourth player to score 20 or more goals in three consecutive Premier League seasons.
Kompany marked his latest return to the City defense by heading a 55th-minute opener before Leroy Sane and Sergio Aguero also contributed goals. City dominated possession, rattling up almost 400 passes before the break and creating a string of chances. And boy was he busy here in his pursuit of an 11th, determined to help City improve on their record of only one win from their last five visits to St Mary's.
"Hopefully he can stay fit".
Among the teams that he has faced at least twice in the Premier League, Sergio Aguero only has a worse minute per goal ratio against Everton (312) than he has against Southampton (264).
The Belgium centre-back, who has suffered a series of injury setbacks over the past three years, was rested against Hull to allow a minor leg problem to clear up, having made only his fourth league appearance of the season three days earlier, in a 2-1 defeat at Chelsea.
All that was left for City to do was see out the opposition in the remainder, which they duly did thanks to the solid defensive work of star performer Kompany. He is an underrated keeper that may not get the notice that he deserves, but I feel he still is a better option that Bravo or Caballero.
The Champions League quarter-finals began this week without City's involvement. They have a good manager and players in all positions. "It depends on the opponent, the pressing, what I see in the training sessions, so we are going to see.I like both to be involved, I have confidence in both of them, so we will see".
After the break, the same theme continued, with the visitors camped in the Saints half while the hosts try to play on the counter-attack.
De Bruyne led the charge as City broke quickly, expertly picking out Sane for the young German to drill low under Forster.
Aguero has scored 10 goals in the 11 games since Gabriel Jesus, who usurped him in the City line-up, got injured at Bournemouth in February.
"Qualifying for the Champions League is so important for the club and the players know that".