For so much of Arsenal and their fateful trip to Manchester City, the spotlight appeared certain to fall on Cristhian Mosquera.
Thrown into the biggest game of the season ahead of the more experienced Ben White, the £13 million summer signing endured a torrid evening against Jeremy Doku and looked every inch a player short of the level required.
Yet while Mosquera struggled, it was manager Mikel Arteta and his second-half decision in attack that may ultimately prove even more costly in the context of the Premier League title race.
Jeremy Doku left Cristhian Mosquera exposed from the very first whistle
© Imago / Sportimage
Arteta's decision to start Mosquera over White always carried an element of risk, but few could have predicted just how badly it would backfire.
Tasked with dealing with Doku on Arsenal's right-hand side, the 21-year-old - who is naturally a centre-back by trade - was immediately overwhelmed by the City winger's pace and directness.
Within the opening ten minutes at the Etihad Stadium, Mosquera had already been forced into two fouls as Doku repeatedly drove beyond him, and the warning signs only intensified as the half wore on.
Every time City worked the ball out to the tricky Belgium international, the north Londoners simply looked vulnerable.
Doku ran rings around Mosquera throughout the opening period, drawing a fourth foul that finally earned the defender a booking, leaving the Gunners walking a disciplinary tightrope before the interval had even arrived.
By the time Arteta replaced him with White in the 74th minute, the damage had already been done. Doku had been City's most dangerous attacking outlet and finished with a deserved 7.4 Sofascore rating after tormenting Mosquera all afternoon - higher than any visiting star on the day.
The Spaniard may argue that White was not fully fit, but if that was the case, then starting Mosquera in a match of this magnitude looked like an unnecessary gamble.
The Eberechi Eze substitution that left Arsenal fans baffled
© Imago / Sportimage
However, as poor as Mosquera's display was, the Gunners still had opportunities to get something from the game.
Eberechi Eze, despite being partly at fault for City's opening goal after backing out of a challenge that allowed Rayan Cherki to burst through and score, still looked the player most likely to make something happen for Arsenal.
The England international was bright whenever he got on the ball, carrying a threat between the lines and coming agonisingly close to equalising when he shifted onto his left foot and curled an effort against the post.
That is why Arteta's decision to take Eze off instead of Martin Odegaard felt bizarre, with some local reports claiming the call left many fans 'baffled.'
Odegaard, while creating four chances, still looked rusty after his recent injury problems and had struggled to impose himself during the second half. The Arsenal captain lacked his usual sharpness, failed to create meaningful openings and looked well short of the player who has driven this side in recent seasons.
Yet Arteta kept faith with him and sacrificed Eze instead, removing Arsenal's biggest attacking threat in the process. From that point on, the visitors looked blunt and predictable, with City comfortably seeing out the game.
If the Gunners are to have any hope of overhauling City, Arteta cannot afford sentiment or loyalty to cloud his judgement. On this occasion, he got the call badly wrong.
Man City now have control of the Premier League title race
© Iconsport / PA Images
The 2-1 victory has now handed Man City complete control of the title race.
Victory over Burnley on Wednesday night would send Pep Guardiola's side to the top of the table, and while their remaining fixture list may appear slightly tougher than Arsenal's on paper, few would bet against them from this position.
City have been here countless times before - they know how to handle the pressure, how to grind out results and how to turn one huge victory into a decisive run of form.
Arsenal, by contrast, now face the psychological blow of knowing they missed a major opportunity.
Losing at the Etihad would always have been damaging, but the manner of the defeat, and the feeling that Arteta contributed to it with two costly major decisions, could leave an even deeper scar.
Mosquera may take the criticism, but it was Arteta's choices before and during the game that could ultimately define Arsenal's season.