We were given almost 70 minutes here to see if we have answer to the Trent Alexander-Arnold puzzle and the truth is that we do not.

This intriguing and absorbing game in the Ruhr valley allowed the Liverpool player to showcase some of his impressive offensive work with the ball as England scored early and dominated an opponent that appeared to have paid too much heed to some of the pre-tournament publicity. We saw the best of the 25-year-old for a short spell.

But this game changed its feel and its shape over time. England were made to feel considerably less comfortable once Serbia found a little forward ambition and tempo and courage. 

Gareth Southgate's team weren't exactly made to hang on but they were they were placed under pressure and when they did Alexander-Arnold lost his sense of assuredness until, with 20 minutes or so remaining, he was taken off and replaced by a more natural central midfield player in Chelsea's Conor Gallagher.

It was the right call by Southgate that came at the time when England needed a partner for Declan Rice with defensive and safety first instincts. 

Gareth Southgate (right) was right to substitute Trent Alexander-Arnold (right) against Serbia

Alexander-Arnold doesn't have those and never will and so the debate goes on. By the end of this game it was England rather than opponents whose world ranking finds them sitting between Peru and Qatar who were looking for the final whistle.

Southgate will perhaps reflect that he made his big call for this opening game and England won it. Nothing to panic about there. The debate is nowhere near settled, though, and it remains to be seen if Southgate is convinced enough to throw it open to the floor again when England face Denmark in Frankfurt on Thursday. That would represent a much bigger call than this one.

The truth is that during this increasingly tense game of football we were presented with much of what we know and rather too much of what we feared. Early on this was a game that was made for Alexander-Arnold. 

Serbia did not attempt to engage in England's half of the field until after Jude Bellingham had powered his beautiful header into their goal. 

This meant that everything that Alexander-Arnold did was with the ball and indeed with the space and the big picture laid out in front of him.

Frankly, we know that he can do that bit. We know that he can move the ball quickly and accurately over long and short distances. We know that he can drop it on to a postage stamp from 40 yards. We know he can take lovely free-kicks. He does all of it brilliantly all of the time for Liverpool from right-back.

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It's the other side of the game that remains harder to call. His defensive awareness has been much discussed and weaknesses exist. He is particularly vulnerable, for example, when players drop off his shoulder. 

As a right-back, that usually happens at either the front or back post. In the middle of the field, a player has to be able to scan at 360 degrees for almost 90 minutes when games are tight and possession is harder to come by.

It wasn't like that here early on and we never really thought it would be. But over time it did become like that and it was then that Alexander-Arnold didn't so much start to struggle but pretty much disappear out of sight. 

Can Southgate risk this happening when the stakes are higher further down the line of this tournament? It's a pertinent question.

For a while here his role was probably as we expected it to be. On the team sheet he was listed as playing alongside Rice at the base of the England midfield but that's not really how it is.

Rice, the Arsenal player, was England's lone defensive pivot and he held his position diligently which allowed Alexander-Arnold to play with freedom. It worked beautifully during that first half an hour that saw England – and the marvellous Jude Bellingham in particular – play the game at their tempo and to their attacking rhythm.

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During this period England's positional fluidity was clear. Alexander-Arnold was confident enough in his role to find space wide on the right, to make runs ahead of the front three and, occasionally, drop back inside his own half. Bellingham, meanwhile, is England's No 10 but regularly dropped deep in search of possession. 

All in all, it was a perfect example of what Southgate means when he says that formations are only really things written down on bits of paper. 

Good teams work off a structural and tactical base in the knowledge that when necessary they can drop in to that shape. But they also have the confidence to interpret it and change it and stretch it on the hoof and as they go. That's what England did so well at times here. It was intelligent football.

But the sobering truth is that over the course of the game it changed. Serbia introduced themselves as an opponent ready to actually engage after about 25 minutes. At that point in the game England's sure and certain control of the game was lost and they never got it back.

It's during periods such as this that questions are really asked of a team's defensive players and it must be said that the England back six didn't come up with all the answers.

Serbia started to find space in between Rice and Alexander-Arnold and the four defenders. Against a better team, England would have coughed up chances.

Alexander-Arnold was just not visible enough during this period and that felt important. Rice, on the other hand, was everywhere. He was cleaning up and tracking runners. His partner not so much and the truth is that it doesn't come naturally to him.

Can such a thing be taught and coached? In all likelihood, yes. Is a major tournament that England are fancied to win the right place to be doing it? Arguably it is not.