The Ballymun Kickhams defender replaces Kevin O’Brien whom he replaced in the first half of the semi-final win.
O’Brien and Ger Brennan were under pressure to hold their positions after early substitutions, the latter being substituted for Denis Bastick at half-time.
Bastick’s introduction saw Cian O’ Sullivan moving back to Brennan’s centre-back spot to mark Colm Cooper.
It was the second time Brennan has been taken off in this year’s Championship but he has done enough in training since the Kerry game to convince Jim Gavin and his management team that he merits a start.
McMahon (26), who made his debut under Paul Caffrey, adds more experience to the back-line compared to last year’s All-Ireland U21 winning captain O’Brien (20) who only made his senior SFC debut this summer.
Dublin, like Mayo, have not named their substitutes’ bench although there is speculation Alan Brogan will be included in the matchday squad, having returned to full fitness before the Kerry game.
Meanwhile, Tipperary’s U21, minor and intermediate hurling management are all understood to have stepped down.
DUBLIN (SF v Mayo): S Cluxton (Parnells); P McMahon (Ballymun Kickhams), R O’Carroll (Kilmacud Crokes), J Cooper (Na Fianna); J McCarthy (Ballymun Kickhams), G Brennan (St Vincent’s), J McCaffrey (Clontarf); MD Macauley (Ballyboden St Enda’s), C O’Sullivan (Kilmacud Crokes); P Flynn (Fingallians), C Kilkenny (Castleknock), D Connolly (St Vincent’s); P Mannion (Kilmacud Crokes), P Andrews (St Brigid’s), B Brogan (Oliver Plunketts/Eoghan Ruadh).
MAYO (MF v Tyrone): M Mulligan (Claremorris); E Doran (Achill), S Cunniffe (Ballaghaderreen), D Kenny (Aghamore); M Hall (Breaffy), S Coen (Hollymount/Carramore), S Conlon (Castlebar Mitchels); V Roughneen (Balla), D O’Connor (Ballintubber); C Loftus (Crossmolina), M Plunkett (Ballintubber), P Prendergast (Louisburgh); D Doherty (Kilmaine), L Irwin (Breaffy), T Conroy (Kiltane).
TYRONE (MF v Mayo): S Fox (Cappagh); C Byrne (Eglish), R Quinn (Clonoe), C McCann (Fintona); S Hamill (Donaghmore), C Morris (Galbally), P McGirr (Errigal Ciaran); R Nugent (Galbally), F Burns (Pomeroy); D Mulgrew (Ardboe), C McKenna (Eglish), R McGlone (Aghaloo); L Brennan (Trillick), D Gallagher (Trillick), S McGrath (Derrylaughan).