Nineteen-year-old Mexico striker Carlos Alberto Vela led the way with a hat-trick, while 16-year-old Jack Wilshere ran the midfield in a performance that must have left manager Arsene Wenger purring.
Manchester United needed two late goals to beat 10-man Middlesbrough 3-1 at Old Trafford while Liverpool, showing 11 changes from the team who drew with Stoke City at the weekend, beat League One (third division) Crewe 2-1 at Anfield.
Gianfranco Zola, who got off to a winning start in his new role as manager of West Ham United at the weekend, tasted defeat on Tuesday when a Hayden Mullins own goal gave Watford victory at Vicarage Road, while Fulham were also on the wrong end of an upset when they lost 1-0 at Burnley, also from the Championship.
Wenger's policy of playing youth players in the League Cup took Arsenal to the semi-finals last season and he had already said he intended to stick with it this year.
Aside from 23-year-old goalkeper Lukasz Fabianksi, Tuesday's team had an average age of not much over 18 and the youngsters rewarded their manager's faith by tearing apart the Championship (second division) visitors.
Nicklas Bendtner, one of the most experienced players in the team at the age of 20, got the first two goals, both after sweeping passing moves.
Vela's treble included a cheeky chip that delighted the Emirates crowd while Wilshere capped a fine individual display by turning sharply and firing in the fifth.
Cristiano Ronaldo marked his first start of the season by heading Manchester United into the lead at Old Trafford but Adam Johnson nodded an equaliser after 56 minutes.
Middlesbrough had Emanuel Pogitez red carded for a bad foul on Brazilian midfielder Rodrigo Possebon after 72 minutes and some poor defending then opened the door for Ryan Giggs and Nani to secure United's progress.
