It was as if his last two appearances, both wobbly in nature, were building to this game and this coming-of-age performance. It was Trent Alexander-Arnold who was twice sucked towards the ball as Romelu Lukaku flicked it on to allow the space for Marcus Rashford to score a brace within the first 25 minutes of the Northwest derby.

And it was the 19-year-old defender who was guilty of the same absent-minded naivety against Crystal Palace last Saturday, when Wilfried Zaha sped between centre-back and full-back to goad a reckless challenge from Loris Karius. The spot kick was converted, and Liverpool, at least until Sadio Mane's second-half goal, were staring another Selhurst Park humbling in the face.

But during the interval, Jurgen Klopp posed a solution to the struggling right-back that became increasingly evident throughout the second half - rather than worrying about the damage Zaha could to to him, Alexander-Arnold had clearly been instructed to push forward and cause the winger problems going towards his own goal.

Zaha, only just returning from injury, struggled to cope with how the extra physical demand of tracking back, and not only did his offensive influence wane as a consequence, but Liverpool's winner - albeit by way of Andrew Robertson recycling it on the other wing before directing into the path of Mohamed Salah - was instigated by a Alexander-Arnold cross.

If Rashford and Zaha represent testing yet inconsistent opponents though, the former a forward only a few stages further along his development than Alexander-Arnold and the latter yet to prove his explosiveness can be equally effective at the elite end of the Premier League, Leroy Sane is a different category altogether.

The 22-year-old is still fine-tuning his craft, but with nine goals and eleven assists in the Premier League has bordered unplayable for substantial periods of the season. For Alexander-Arnold to contain him in the first leg of Liverpool's Champions League quarter-final with Manchester City, the England U21 would need to excel in both aspects - offensive and defensive - of the full-back trade, and use his intelligence to seamlessly gel them together.

Perhaps aided by Pep Guardiola's decision to use the German international as part wing-back, part winger in an ill-fated formation change, it was Alexander-Arnold who dominated this key individual battle against one of the Premier League's top attacking performers this season, in a game of crucially high stakes.

At times in the first half, it even felt as if Alexander-Arnold was the exciting young player held in such high worldwide regard, and Sane who was still learning from his mistakes during a first full season at first team level. The Liverpool academy product confronted the City star high up the pitch, before pushing him so far back City's defence was forcibly reshaped from a back three into a back five.

Of course, this was a good night for Liverpool and a bad night for City, one where Sane was their only obvious offensive outlet on the break and seemed to struggle with just how much of the play was being funnelled through him - although that did raise the suspicion that Alexander-Arnold had been targeted as Liverpool's weakest link.

Far from vulnerable though, the youngster made the most interceptions, the most clearances, had the most touches of the ball and won the most tackles of any Reds player - defensive focus was met with real readiness and responsibility on the ball.

Let's not forget that fortune has favoured the defender here, who Transfermarkt value at just £7.2million. It's highly possible that the more defensively dependable Joe Gomez would have started this fixture, against such an attacking team, had he not limped off injured on international duty.

It's also less possible but by no means impossible that the more experienced Nathaniel Clyne could have been thrust back into the starting XI for this huge clash, had he returned to training a little earlier after his huge injury layoff.

But being a young player at a club of Liverpool's stature is all about embracing the chances that come to, and learning from your mistakes quickly. During the course of the last three games, which in themselves have been an interesting microcosm of Alexander-Arnold's development, the tenacious teenager has certainly done that. The question for Klopp now, is who should be his first-choice right-back next season. Let us know by voting below...

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