Aguero then helped himself to his second of the night and it appeared as though the Sky Blues would run away with it, but the Saints were able to pull a goal back through Jack Stephens. Nonetheless, it was a comfortable evening for Pep Guardiola's men.
Leicester followed up their record-breaking win over Southampton with another impressive display, as Brendan Rodgers' men overcame League One side Burton 3-1. Kelechi Iheanacho opened the scoring for the Foxes from a Youri Tielemans pass, before Tielemans doubled the away side's lead.
Liam Boyce gave the home side hope, but Rodgers' men were able to add a third through James Maddison and book their place in the next round.
The Toffees hit the woodwork twice, before Mason Holgate's header broke the deadlock. Richarlison added a second to seal the win and ease the pressure on Marco Silva.
Elsewhere, Oxford United overcame fellow League One side Sunderland on penalties, after the match ended 1-1. Robert Hall gave Oxford the lead, but the away side were able to draw level late on and take the game to penalties. Oxford goalkeeper Simon Eastwood was the hero, as the home side booked their place in the quarter-finals with a 4-2 win in the shootout.
And Colchester overcame their League Two counterparts Crawley Town, as they prevailed 3-1.
Carabao Cup Fourth Round Results:
|Manchester City 3-1 Southampton|
|Burton 1-3 Leicester City|
|Everton 2-0 Watford|
|Crawley Town 1-3 Colchester|
|Oxford United 1-1 Sunderland (4-2 Pen)|