And Sterling completed his hat-trick and secured the three points just before the hour mark when he crept in behind Daryl Janmaat to collect Bernardo Silva's exquisite through ball and slot past Watford goalkeeper Ben Foster.
The opening half was a poor one for City in front of goal as they continously squandered possession in the final third with bad decision making and woeful shooting which saw the half ended goalless.
Eighteen for the season in all competitions, as well as 15 assists. Watford seemed content to get every player back behind the ball, setting themselves up to hit their opponents on the counter through the likes of Isaac Success and Andre Gray.
Following prolonged discussions between the match officials, the goal was awarded despite Sterling being in an offside position when Aguero touched the ball into his path, because Janmaat played it against the England winger's shin for the ricochet into the net.
'I happened to get the luck, so I am happy with that.
But after such a hard opening period, no-one would have expected that the game would have been settled decisively in City's favour in the opening quarter of an hour after the break.More news: Former Trump attorney: Mueller’s "an American hero", investigation not a "witch hunt"
"If we have made mistakes we will be punished".
Financial regulations such as salary caps were first introduced in the National Basketball Association in 1984, and United States owners in the Premier League have subsequently come to expect similar measures to be taken in the English top flight, with any breaking of the rules to be punished.
Cardiff's win was not enough to take the 18th-placed side out of the bottom three but they are only two points behind Burnley and Southampton (30 points) while Brighton joined Palace on 33.
Manchester City won the Premier League in the 2017-18 season and are now seated at the top of the table.
Sterling said afterwards: "I don't know exactly what it was but i was praying they'd give it to us".
There seems, however, no hope for Fulham under caretaker manager Scott Parker, after their defeat at Leicester, whose own new boss Brendan Rodgers was grateful for Vardy's late double.
"So, I am so sorry, apologise, to Javi (Gracia) and the club Watford if the first goal is offside, but we made an incredible game and we played good in the first half".