Euro 2020 is the first major tournament in which five substitutes can be used by each team.
The measures were announced by Uefa in March in order to help ease player workload at the end of an intense season compressed by the coronavirus pandemic.
Almost all top-level football typically deploys three subs but that has changed in competitions like the Champions League this season, where five were also used.
VAR will also be used after being brought in for the first time at the 2018 World Cup.
VAR decisions served up several moments of high drama in Russia three years ago, with holders Germany’s hopes dashed in the group stage after Kim Young-gwon’s stoppage-time goal for South Korea was awarded, having been initially ruled out for offside by the linesman.
Iago Aspas benefitted from a similar last-gasp video intervention as his flick was deemed onside after a review, seeing Spain defeat Morroco to take top spot in their group.
Meanwhile, France received a slice of luck in their opening game when the referee opted to award a penalty to Antoine Griezmann after consulting the pitchside monitor and the eventual champions went on to beat Australia 2-1.
The technology will no doubt play an influential role this summer, with moments of ill-discipline, contentious handballs and various penalty appeals to be scrutinised in detail.
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