Christopher Nkunku scored a hat-trick as Chelsea thrashed fourth-tier Barrow 5-0 to reach the last 16 of the Carabao Cup on Tuesday as a much-changed Manchester City edged out Watford 2-1.

Nkunku now has six goals in seven appearances this season, but the Frenchman has still been unable to nail down a regular place in Enzo Maresca's side.

Maresca made 11 changes from the team that beat West Ham 3-0 on Saturday but could still start around US$533 million worth of talent.

João Félix was another of the Blues' big money signings to shine. His scooped pass set up Nkunku for opener. Nkunku then flicked home a second before Félix's free-kick hit the post and rebounded in off Barrow goalkeeper Paul Farman.

Pedro Neto tapped in Mykhailo Mudryk's cross for his first Chelsea goal. Nkunku sealed his first hat-trick for the club when he dispossessed Farman and rolled into an empty net.

Meanwhile, Manchester City began what is likely to be many months without key midfielder Rodri after he suffered suspected knee ligament damage in a fiery 2-2 draw against Arsenal in the Premier League on Sunday.

A little over 48 hours on from that top-of-the-table clash, City were in action again and Pep Guardiola made nine changes, including a debut for 16-year-old Kaden Braithwaite.

Jeremy Doku, one of the two to retain his place, fired in the opening goal from Jack Grealish's pass after five minutes.

Rodri's absence could mean a more prominent role for Matheus Nunes and the Portugal international blasted in his first goal since joining City a year ago. (AFP)