Watford had lost their seven previous league meetings with City, but they were putting up a very resolute display in defence, although Foster was called upon right at the end of the half to push behind a snap-shot from a tight angle by Aguero as City tried to find the all-important breakthrough.
The opening goal came within a minute of the restart amid considerable offside controversy.
The third goal was Sterling's 15th of the season in the Premier League, and he is just three behind teammate and leading marksman Aguero.
"I'm not too much concerned or anxious about what people say if we win the title just because [of] what happens now with UEFA [and] they do not give us credit for what we have done". The goal was initially ruled out for offside by the linesman but the decision was overturned by referee Paul Tierney; a controversial moment to say the least. "In my head, I am hoping and praying (that the first goal would be awarded)".
"I happened to get the luck, so I am happy with that".
After that, we have the global break and we come back and it will be "guys, one month and a half" and let's go.
On an unhappy return to his old St Mary's stamping ground, Pochettino, serving the first of a two-match touchline ban, could hardly credit how his side capitulated to two late goals in five minutes from Yan Valery and James Ward-Prowse.
And with Saturday's home game versus Watford followed by a 21-day break to their next league encounter, after which City's schedule is relentless, Guardiola acknowledges the importance of taking another big stride at the Etihad Stadium.
"In the first half we had a very good performance - better defensively because we were well organised", manager Gracia said.
Reports revealed that UEFA and the Premier League are looking into a few issues with City regarding FFP regulation breaches, manipulation of the amount of money the club made, and how they've signed underage players.
Tottenham's Harry Kane reacts as Southampton's Maya Yoshida looks on during their Premier League match St Mary's Stadium in Southampton March 9, 2019.
Sterling said afterwards: "I don't know exactly what it was but i was praying they'd give it to us". The three goals were fantastic but he can do better.