There was a glaring reveal towards the end of Manchester City’s deserved victory over Atlético Madrid on Tuesday. With Jack Grealish on the floor Ángel Correa smashed the ball into the No 10’s face. It was on the touchline. It was right by Pep Guardiola. And Manchester City’s manager did not like it at all.

So: he entered the pitch and shoved Correa. He stuck up for his player. Bravo. He might also have been booked or even sent off. But Istvan Kovacs ignored the seething 51-year-old and booked Correa.

Here, though, was what poker players call the “tell” and a collector’s item as Guardiola has been über-serene recently, zen-like since around this time last season. Yes, he is still seen frantically semaphoring on the touchline or unloading the mother and father of rollockings to, say, Raheem Sterling (it is often Sterling) directly after the forward has finished the latest sublime City goal. Or giving John Stones or Aymeric Laporte an impromptu lecture on some geometric nuance of centre-back play they must apply when stepping into midfield.

Yet these moments are kept to his own players. Long gone are the days when the head coach’s lack of control over his side and himself had him in curt (some might say rude) form with BBC reporter Damian Johnson following a 2-1 win over Burnley in January of his first season with City in 2017. Two weeks later came the admission that “maybe I am not good enough” for City on the eve of a 2-2- draw at Tottenham. And directly after that result he showed more prickles when another reporter from the BBC – Guy Mowbray – was challenged, oddly, that “the first question is about the referee? It’s BBC – BBC has prestige.”

Guardiola has calmed since. Three Premier League titles, a record 100-points, a domestic treble and a remodelling of how the game is discharged on these shores – the goalkeeper as deep-lying schemer, for example – are prime reasons why.

It meant that last year when City hit crisis point after a 1-1 draw with West Brom in December that left them trailing leaders Liverpool by eight points Guardiola’s serenity allowed him to redraw the plan (in essence, pass more, run less in possession) and a 15-match streak of victories swept his side to the championship.

Pep Guardiola tries to hold back Jack Grealish as things get heated at the Etihad
Pep Guardiola tries to hold back Jack Grealish as things get heated at the Etihad. Photograph: Tom Jenkins/The Guardian

The sight, then, of Guardiola mixing it with Correa on Tuesday night, in a deliciously spiky Etihad Stadium atmosphere, was instructive. A manager protecting his players is how it should be and, if he went a little far, this is the Champions League quarter-finals and the stakes are sky-high. But, he should be careful. Asked about the incident later, Guardiola brushed it off while stating his players will have to be calm at Wanda Metropolitana. This applies to him, too. The sight of Guardiola, directly after his own contretemps, pulling away an upset Grealish was comical.

City are currently in the most intense, zero-sum period of the Guardiola project. Following this first leg, Liverpool are Sunday’s visitors in a contest that may define the destination of the title. Jürgen Klopp’s team arrive a point behind, having played the same 30 matches. This, then, is the first of an eight-match shootout for the championship. Stones, signed by Guardiola in his first summer of 2016 and thus a veteran of successful City campaigns, is dismissive of it being decisive.

“I don’t think so,” the defender says. “Obviously it’s an important game, we’re first and second in the table – everyone knows that. This week is vital for us in how we prepare and stay calm because we’ve been in situations like this before. Three years ago it came down to the last game [beating Brighton to be champions]. So we’ve been in these situations before and the experience of that time we definitely learned from.”

Stones has a point but if there is a victor at the Etihad confidence and momentum levels will rocket. A second meeting with Liverpool looms in the FA Cup semi-finals a week on Saturday but before that is the return leg in Madrid. Guardiola says City go there to win despite the 1-0 advantage yet there is another intriguing stick-or-twist side plot.

Diego Simeone’s side are guaranteed to use all the ploys they can. So, does Guardiola turn to his prime master of the darker arts to meet this challenge head-on? Or does he leave Fernandinho on the bench and refuse to engage how the enemy would like? As Stones says: “We knew how they’d set up and try to frustrate. I thought how we moved the ball and kept our patience during the game was key.”

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Patience: this is what Atlético test. Guardiola has to ensure his cracking of cool in the opener is a one-off because Simeone’s men may target his and his side’s calm again from the first whistle on Wednesday.