Pupil Messi teaches old Barcelona master Guardiola a lesson

The irony of how superbly Lionel Messi played in Barcelona's 4-0 defeat of Manchester City simply linked to the fact that he's beginning to treat his former mentor a trifle too robustly.

• Match report: Messi hat-trick punishes City slips

Pep Guardiola has come back to the Camp Nou twice as a rival coach and during two aggregate 7-0 defeats it is his star pupil, Messi, who has scored five times, got an assist and won a penalty.

Not what you'd call gratitude.

But, all joking aside, what stood out about the Argentinian's hat-trick (taking him to six goals in the UEFA Champions League already this season) was where he scored them from and where he positioned himself during the match.

The irony is that when Guardiola decided to make Messi a central attacker rather than a winger, he always used the expression: "He's our best player and the more often we use him closer to the opponents' goal, the more often he's likely to score."

The Guardiola-Messi tandem ripped up record books. Brilliant maestro and brilliant favourite pupil.

Whether you want to call his position 'false nine' or withdrawn striker, it turned him from an important weapon in Barcelona's armoury to an irresistibly prolific force of nature.

But times change and so do positions. Messi was still the lead central forward when Luis Suárez arrived at the Camp Nou in 2014 but between the Argentinian and the Uruguayan they agreed that the new boy needed to play in the No9 position and that Leo would return to the right wing.

The fabled 'treble' of trophies followed within five months of that decision.

Since then, however, Messi has been enjoying many more plaudits for his brilliant 'quarterback' passing from midfield.

• Match as it happened

With Xavi Hernández no longer running the show in the middle, Messi drops back from the front line to create 'superiority' of numbers and to help overwhelm opponents' playing schemes.

He's brilliant at it, naturally. But there's a cost.

Barcelona can look unbalanced up front if the 'MSN' trident becomes two players, there can be a lack of width and while Messi's passing range and ability to 'arrive' in the box is highly threatening his goal ratio has dropped. And Barcelona's playing style has most definitely evolved.

In this 24-carat display he was, once more, a predatory central striker.

Penalty-box chaos when Fernandinho slipped and fell? Messi on the penalty spot to react most sharply.

City losing possession in front of their penalty area in the second half? Messi near enough to the front line to pick up possession, take a few short steps and fire past Willy Caballero.

Hat-trick goal? Barca's No10 dancing across the penalty box to slot in from Suárez's assist.

• Messi and Ronaldo goal for goal

"He was totally relaxed, it was like he was playing in the school playground," said Luis Enrique.

Perhaps because, this time, he was situated where poor old Guardiola first determined he was most able to wreak havoc on rivals. Perhaps last night the Catalan wished he'd never unleashed this scoring monster. You wouldn't blame him.

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