Allen was ruled out of Monday's opener against the USMNT, which saw a late Gareth Bale penalty earn a 1-1 draw, but manager Page – after confirming that he is ready to be involved again – has named the Swansea City midfielder on the bench. Kieffer Moore replaces Daniel James in the one change from that side, with Bale likely to switch to a wide role.
“The medical team have been exceptional and they’re the reason he’s now fit,” Page said on Allen.
“We were all concerned about him, the way he kept breaking down. He’s had to meet targets along the way, he’s met every one. If we’d played him in game one and he’d broken down he would have been completely out.
“We could have pushed him for USA, but due to the confidence we have to get out of the group I want him for the long-term.”
For Iran, first-choice goalkeeper Alireza Beiranvand is out after suffering a concussion in the 6-2 thrashing by England on Monday, with back-up stopper Hossein Hosseini starting. The experienced former Brighton winger Alireza Jahanbakhsh is again only among the substitues.
Wales XI: Hennessey; Mepham, Rodon, B Davies; Roberts, Ampadu, Ramsey, Wilson, N Williams; Bale (C), Moore.
Iran XI: Hosseini; Rezaeian, Pouraliganji, Hosseini, Mohammadi; Gholizadeh, Nourollahi, Ezatollahi, Hajsafi; Azmoun, Taremi.