The most notable element of Sergio Aguero looking on as an unused substitute when Manchester City won at Old Trafford in December last season was how unremarkable it seemed.

A month earlier, Aguero claimed a place in the history books by scoring in City's 4-2 Champions League win over Napoli – becoming the club's all-time leading goalscorer – but that lofty status offered no guarantees.

Ever since Gabriel Jesus' arrival from Palmeiras in January 2017, the Argentine's status as the number one striker at the Etihad Stadium had been under threat to an extent it never was in the previous five and a half years.

Barring any late fitness concerns in the hours before a Manchester derby that looks set to prove pivotal in the destiny of the Premier League title, there is no doubt who will lead Pep Guardiola's attack on enemy territory this Wednesday.

Jesus tests the old messiah

It is something of a quirk that Aguero, one of the English top flight's leading strikers, has not played at the division's most famous ground in the competition for four years.

For Guardiola's first derby in charge of City in September 2016, he was suspended – the first of two bans for violent conduct acquired before the turn of that year.

Those moments of indiscipline spoke of a player frustrated by the new demands of his manager's feted playing style and an early season goal glut, including hat-tricks versus Steaua Bucharest and Borussia Monchengladbach in Europe, was met with qualified praise.

"He has to know that behind him there is a team that is going to help him if he is going to help us. That is what I have to convince him," Guardiola said.

Jesus, it seemed, needed very little persuasion. By the start of February 2017, Aguero was on the bench as City's other striker started three consecutive Premier League matches.

Making hay with the centurions

In the third match, Jesus suffered a broken metatarsal at Bournemouth, meaning Aguero had a chance to regain his old status and the forward duo ended Guardiola's first season in charge starting together.

Aguero tore into 2017-18, again in tandem with Jesus, before a broken rib suffered when his taxi crashed following an evening out in Amsterdam checked his progress – an episode that appeared entirely unhelpful for a man looking to win his boss around.

In the same month that Jesus got the nod at Old Trafford, Guardiola praised his high pressing as "the best in the world", despite a fallow period in front of goal.

City's strikers continued to dovetail with their fitness problems as the Brazil star sustained medial ligament damage and Aguero stormed into 2018, hitting 15 goals and notching two hat-tricks in the period up to and including a 3-0 EFL Cup final win over Arsenal.

Injury struck once more, with a knee problem leaving Aguero in a race to be fit for Argentina's shambolic 2018 World Cup campaign. When champions City needed a stoppage-time goal to reach 100 points on the final day of the season at Southampton, it was Jesus who stepped forward.

Top dog leading by example

When Aguero's match-winning brace against Chelsea in last August's Community Shield was brought up at the post-match news conference, Guardiola beamed.

"We were really impressed when he arrived [for pre-season training]," he said. "With his physicality, maybe he [usually] needs a little more time but he arrived so sharp and so good."

Now 200 goals into his City career, Aguero was breaching new ground and emphatically restating his worth.

A haul of 30 in all competitions has yielded a PFA Player of the Year nomination, while two trebles in as many weekends against Arsenal and Chelsea brought him level with Alan Shearer as the most prolific hat-trick scorer in Premier League history.

But goals only tell a part of the story. According to Opta data, Aguero is winning possession in the final third more often than in his previous two seasons under Guardiola.

It is the same story in terms of interceptions and tackles made, while he has never claimed more than his eight assists so far in a Premier League season. As Leroy Sane and record signing Riyad Mahrez struggle for starts amid murmurings of discontent, Aguero is the example of what must be done to win Guardiola around.

As City toiled in vain during last week's Champions League epic against Tottenham, Aguero was everywhere – scoring, relentlessly running at defenders and setting up Raheem Sterling for the goal that wasn't.

He felt the natural choice to captain last weekend's domestic rematch with Spurs as Vincent Kompany recuperated. There was another assist, to give former ballboy and current team-mate Phil Foden a moment he will never forget.

As an understandably fraught Ole Gunnar Solskjaer talks slightly spuriously of "United DNA" ahead of a fixture his team do not need, City will confidently take their cues from an attacking leader and club great aiming to improve upon a record of four goals in three derby outings at Old Trafford.

Whatever they go on to accomplish over the coming weeks, Aguero is almost certain to play a decisive role. Where it was once hard to envisage a successful Guardiola team with him as its fulcrum, it is once again impossible to imagine the Premier League champions at their best without Aguero.