Some are entirely new - teenage midfielder Pedri after his excellent season with Barcelona, for example - and some are those brought back into favour after previously falling out of the first-team scene for Spain; captain on the night Jordi Alba being a case in point here.
The forward line was perhaps the most open of all: While Adama Traore could feasibly be considered just an impact sub at this point, any of three could have started the No9 role, while Mikel Oyarzabal has the most caps of any of the wider options.
Still, Dani Olmo was given his chance from the start, playing left of the front three but with plenty of licence to roam and scheme - and was arguably one of the game’s top performers as Spain were held to a 0-0 draw by Sweden.
Early on, his movement and willingness to drift into different areas of the pitch were very much in evidence, a familiar sight to anyone who has watched the 23-year-old fill a variety of roles for Julian Nagelsmann at RB Leipzig this past season.
While coming deep, tracking his man to the full-back zone when required and seeking possession infield were all part of his intent to help Spain’s build-up play, the more important aspect of Olmo’s movement was his desire to break into the box and run beyond the striker.
With Alvaro Morata often occupied by two centre-backs or dropping out of the front line to make room for others, the wide forwards getting into that central zone was important - and Olmo did so far more than Ferran Torres.
It wasn’t only his off-the-ball impact which stood out, but his ongoing threat to the Sweden goal.
Early on, a drilled effort flew over the bar from range. Soon after, some quick feet saw him escape a tackle and win a free-kick, which led to another chance for Spain. The best chance of the match in those early stages also fell the way of Olmo: another run in off the left flank saw him pick up a great position, but a downward header after a cross from the right was well tipped-away by the goalkeeper, Robin Olsen.
Undeterred, the efforts kept coming: a fierce and swerving strike before the break which was saved, just about, plus a drilled shot through a crowded penalty area in the second half which was certainly goalbound - until one of many outstretched Swedish boots diverted it away to safety.
Luis Enrique made changes to half his outfield line-up in the second half in pursuit of the elusive winner, with all three of the starting forwards predictably withdrawn in favour of fresher legs and different ideas. Olmo wasn’t exempt, but he wasn’t first off, either.
He has likely done enough to earn another starting chance, unless his manager is so frustrated with failing to take three points that he feels wholesale switches are required.
Ferran Torres offered little, Alvaro Morata was actively poor, spurning Spain’s best chance with a simple one-on-one steered wide. Those two seem the more likely to be replaced, given the goal record Gerard Moreno in particular has offered this season.
With five shots and two chances created, Olmo was by far the most regular threat and the most convincing one in the team.
To put it another way, of the 15 efforts Spain managed in the 90 minutes, the Leipzig man was in one way or another responsible for almost half of them.
With Slovakia and Poland yet ahead, Luis Enrique’s side will remain favourites to progress, but the template has also now been set for those teams to follow in trying to get a result of their own.
More guile, more tempo and much more of a clinical edge will be needed for significant Spain improvements to be seen, and Olmo is likely to remain a big part of the plan.
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