Pep Guardiola's men made light work of a Watford defence that had been impenetrable in the Hornets' previous three games, with Gabriel Jesus, Nicolas Otamendi and Raheem Sterling all joining Aguero on the scoresheet.
Aguero made it nine goals in five games against Watford and with two simple first-half strikes from close range and a brilliant second-half solo goal, while Jesus scored his 11th goal in 13 Premier League starts since joining the club in January.
The game was reminiscent of City's previous visit to Vicarage Road in May, when Jesus scored and Aguero got two in a 5-0 win, and Watford manager Marco Silva must prepare his reeling troops to bounce back when they travel to Swansea City and West Brom before the end of September.
Meanwhile, Guardiola can reflect on a week in which his side scored 15 goals without reply ahead of four games in three different competitions over the next two weeks.
Watford withstood City's early pressure, with goalkeeper Heurelho Gomes saving well from Fernandinho and Christian Kabasele making a superb tackle to deny Aguero a one-on-one after 18 minutes.
Watford's Brazilian forward Richarlison glanced a header wide of the post after 24 minutes but the breakthrough arrived at the other end three minutes later when Kevin De Bruyne floated a free-kick onto the head of Aguero, who made no mistake from five yards out.
Four minutes later, Jesus skipped down the left flank before feeding the ball to David Silva inside the box and the Spaniard squared it across the face of goal where Aguero arrived unchallenged to poke the ball home.
City's South American forwards made a mockery of Watford's burgeoning reputation for being a tough team to break down by making it 3-0 after 37 minutes when Aguero dribbled to the edge of the box and threaded a pass to Jesus, who picked his spot in the far corner of the net and dispatched the ball clinically.
Richarlison curled a shot just wide of Ederson's goal as Watford looked to re-assert themselves early in the second half but Gomes remained the busier of the two keepers and he saved Silva's powerful rising shot brilliantly on 62 minutes.
But Gomes' hard work was undone one minute later when Silva sent over a cross that evaded the yellow shirts in the box and picked out Otamendi, who powered a header beyond the goalkeeper to make it 4-0 with just over an hour played.
Etienne Capoue blazed a free header over the crossbar 19 minutes from time, before Aguero scored the pick of the goals when he danced through Watford's defence and rolled the ball into the net.
Sterling than completed the rout, slamming home an 88th-minute penalty after he was brought down in the box by Kabasele.
