The goal came just three minutes after Aguero had opened the scoring.
David Silva found himself in space down the left and as he got to the byline Watford failed to clear his low cross, allowing Aguero to tap home from close range.
That goal takes the Argentine to five in all competitions so far this season.
Check it out for yourself below.
Aguero second goal vs watford #WAIvMAN #Aguero #Mancity #Cmoncity pic.twitter.com/xNDHtBOpCd
— Jashan sandhu (@jashansandhu99) 16 de septiembre de 2017