Enda Smith blazed narrowly wide within fifteen seconds of the resumption as Dublin availed of a rules infringement in the 39th minute with Scully popping over the resultant free.
Points followed through McGinnis and Charlie McMorrow as the away lead stretched to sixteen points before the hosts finally found their two-point range through Murtagh in the 44thminute.
A brilliant point on the counter-attack, finished by Breathnach, ensured the Dubs maintained a threat in attack but a goal at the opposite end from Ruane in the 50th minute offered hope to the home faithful.
Cregg and Caelim Keogh added points soon after as Dublin came under increasing pressure but the cool heads of Ciaran Kilkenny, Scully and Howard saw them take the sting from Roscommon’s comeback.
Alex Gavin’s point in the 63rd minute was equally significant as the home challenge wilted and Dublin pressed home their dominance through late points from McGinnis and Ross McGarry.
Scorers – Dublin: L Breathnach 1-1; S Bugler (1 P2), N Scully (1 P2, 2f) 0-4 each; P Small (1 P2, 1f) 0-3; E Kennedy (P2), H O’Sullivan (F2), K McGinnis 0-2 each; C McMorrow, A Gavin, R McGarry 0-1 apiece. Roscommon: D Cregg 1-1; D Ruane 1-0; D Murtagh (P2) 0-2; R Heneghan, C Keogh, E Colleran, S Lambe 0-1 apiece.
Dublin: H O’Sullivan; E Murchan, N Doran, D Byrne; A Gavin, C McMorrow, E Kennedy; P Ó Cofaigh Byrne, B Howard; N Scully, S Bugler, C Kilkenny; P Small, K McGinnis, L Breathnach. Subs: L Smith for Murchan (Temp, 2-3), G McEneaney for Kennedy (53), N O’Callaghan for Small (58), J Lundy for Breathnach (63), R McGarry for Kilkenny (68), L Smith for Murchan (69).
Roscommon: C Carroll; P Gavin, C Keogh, C Neary; E Ward, R Daly, S Lambe; K Doyle, R Fallon; D Ruane, E Smith, C Hand; D Murtagh, D Cregg, R Heneghan. Subs: J Duggan for Fallon (half-time), C Lennon for Hand (43), E Colleran for Heneghan (46), N Higgins for Daly (58), P Carey for Ruane (62).
Referee: Conor Lane (Cork).