Thrown in at the deep end when selected full forward Denis O’Leary arrived late, O’Sullivan, an Inniscarra U-21 player, hit a glorious hat-trick of goals as Muskerry stormed back to triumph after a terrible start.
Lightning fast goals from Donogh Duane and Noel O’Callaghan, propelled Duhallow into a 2-3 lead before a shell-shocked Muskerry side managed to get on the scoresheet.
The free-taking expertise of Cronin, who hit four points in quick succession, was primarily responsible for easing Muskerry back into contention.
Duhallow were leading by 2-6 to 0-8 when full forward O’Sullivan struck for the first of his three goals in 25th minute and the sides were level a minute later when left half forward John Hurley pointed for Muskerry.
Duhallow responded well, however, to the now, more stern challenge confronting them, with home boy Noel O’Callaghan grabbing his second goal.
But not to be outdone O’Sullivan pounced for his second at the other end on the stroke of half time to leave it all square at 3-6 to 2-9 at the break.
The sides were subsequently level of three occasions before Muskerry edged in front for the first time in the 47th minute when, after Wayne King and Crowley had given Duhallow a two points advantage, the mid-Cork centre forward Tom O’Mahony soloed all of 30-metres before rifling the roof of the net with a thunderous drive.
They were level for the fifth time when Crowley pointed another free for Duhallow ten minutes from time and at this stage of the evenly-balanced proceedings it appeared that this game would go down to the wire.
But unlikely hero O’Sullivan, whose name wasn’t even in the list of substitutes, swung the delicately poised contest in Muskerry’s favour with the completion of his hat-trick in the 55th minute.
Scorers for Muskerry: M. O’Sullivan 3-1; T. O’Mahony 1-2; T. Cronin 0-8 (0-7 from frees); J. Hurley 0-2; J. Russell and F. Kelly (free) 0-1 each.
Duhallow. N. O’Callaghan 2-1; D. Duane 1-0; D. Crowley 0-6 (0-4 from frees); S. Whelan 0-2; W. King, K. McCarthy and G. Buckley 0-1 each.
MUSKERRY: R. Byrne (Blarney); J. Carey (Inniscarra), D. Murphy (Ballincollig), D. Twomey (do); J. Hughes (Blarney), N. Buckley (Aghabullogue), P. Kelleher (do): T. Cronin (Eire Og), F. Kelly (Ballincollig); N. Brennan (Eire Og), T. O’Mahony (Cloughduv), J. Hurley (Blarney); J. Shanahan (Cloughduv), M. O’Sullivan (Inniscarra), D. Corkery (Cloughduv). Subs. S. O’Donoghue (Blarney) for Kelleher; J. Russell (Grenagh) for Brennan; R. Ryan (Ballincollig) for Shanahan.
DUHALLOW: A. Walsh (Kanturk); D. McCarthy (Millstreet), C. Buckley (Banteer), C. O’Keeffe (do); B. O’Leary (Newmarket), D. Twomey (Millstreet), N. Cronin (Kilbrin); W. King (do), G. Buckley (Banteer); K. McCarthy (Millstreet), S. O’Riordan (Kilbrin), S. Whelan (Tullylease); N. O’Callaghan (Kilbrin), D. Duane (Lismire), D. Crowley (Kilbrin). Subs. M. O’Connor (Banteer) for Duane; E. Casey (Kilbrin) for O’Keeffe.
Referee: D. Farrell (Ballygiblin).