Manchester City manager Pep Guardiola has admitted that the football club is still "far away" from mounting a challenge for the Champions League gong, European club football's biggest prize.
First Silva's through-ball sent De Bruyne through and he squared for Sane to sweep past Forster, then Aguero nodded in his 11th goal in 11 games.
Victory for the Citizens at St Mary's will see them move seven points clear of Manchester United, who will have played two games less and all but guarantee their spot in the top four, with six games left to play after this.
"Vincent is a central defender who doesn't only win all the duels, but reads the game and passes well", Guardiola told BT Sport.
"Manuel [Pellegrini] last season missed him a lot last season and we have missed him a lot [this season]". Hopefully we got that experience there and it'll help us next season. For example the fans are always flawless, I love that, and you know the club is awesome, the club supports everybody. They have spent a fortune on players but it has has not panned out the way their Spanish coach would have wanted. A recent draw with Arsenal and defeat by Liverpool have not made their fans very happy.
Mid-table Saints failed to create many chances against a City side well marshalled by Kompany, with Dusan Tadic shooting over before the break.More news: Napa ranks high in Lung Association's clean air report
He said: "My feeling before that was he was just waiting to score a goal".
Kompany also caught the eye with his faultless defensive display, which pleased City manager Pep Guardiola.
Belgian playmaker Kevin Debryune provided two assists for the second and third goals in the encounter which saw Nigeria star Kelechi Iheanacho replace Aguero with three minutes to play.
City face off against Arsenal on Sunday in the FA Cup semi-final and Sane will be keen to inflict more woe on the out-of-form Gunners after finding the net against them in every game so far this season. After that it wasn't easy, but we could use the counter-attack and had space between the lines.
"This result is so important for our qualification for the Champions League", said Guardiola, whose side host neighbours United in their next league game. They had a good recovery of the ball, high up the pitch.