Don't mess with the FA cup- Plymouth teaches slot a lesson.

Arne Slot’s seamless succession to Jurgen Klopp as Liverpool manager has shown he is not only an outstanding coach but a fast learner – but he was given a harsh lesson in one of the game’s oldest rules on a wild afternoon in Devon.

Never play fast and loose with the grand old FA Cup.

The sight of Plymouth Argyle, bottom of the Championship, embarrassing Premier League leaders and the previously all-conquering Liverpool with this fourth-round victory was a compelling response to those who would to attempt to downgrade the magic and history of the competition.

And for Slot, it proved to be the first wrong move in a stellar start at Anfield, proof that you try to play tricks with the FA Cup at your peril.

Liverpool’s head coach will point, with some justification, to priorities elsewhere having reached the Carabao Cup final by sweeping Tottenham Hotspur aside on Thursday.

They also have the chance to cement their healthy lead in the Premier League against Everton in Goodison Park’s final Merseyside derby on Wednesday.

This cannot disguise the fact, however, that Slot and Liverpool got this wrong.

In making 10 changes here, Slot was guilty of taking the FA Cup and Plymouth Argyle lightly, the result being acute embarrassment.

Liverpool still had plenty of experience and quality in their line-up, perhaps enough to beat a struggling Championship side, with the international trio of Luis Diaz, Diogo Jota and Federico Chiesa in attack.

This whole experience, though, was as much of a let-down for Slot’s team as it was a glorious one for Plymouth.

And those three forwards – Diaz, Jota and Chiesa – were particularly disappointing, playing as if the outing was a chore rather than a high-profile FA Cup tie.

Questions can also be asked elsewhere about Slot’s approach.

Slot did not even have the safety net of Mohamed Salah, Virgil van Dijk, Ryan Gravenberch, Alex Mac Allister, Dominik Szoboszlai, Ibrahima Konate, Cody Gakpo and Andrew Robertson on the bench, just in case things went wrong for Liverpool.

As they did, quite spectacularly.