Dennehy takes full advantage of Longford errors
Two second-half errors proved costly for Longford Town as Shamrock Rovers advanced.
After dominating the first half Town fell behind nine minutes after the break as Rovers broke the deadlock against the run of play: Neale Fenn's effort came off the bar, Gary Twigged hooked it back and Town defender Chris Deans headed into his own net.
They doubled their advantage in the 71st minute when Billy Dennehy's free-kick from the edge of the box slipped through the hands of Town 'keeper Aaron Shanahan.
Town, though, didn't give up the fight and pulled a goal back in the 79th minute when in a crowded box John Lester got to the end of Mark Salmon's cross to toe-poke home.
Rovers were unconvincing as First Division Town really put it up to their illustrious opponents and deserved more.
In the 34th minute Town had calls for a penalty turned down after Hynes' 25-yard shot seemed to hit the arm of Aiden Price.
As half-time approached the home side pressed for the opener. Mark Salmon capitalised on a mistake by Chris Turner, broke down to the end-line and crossed into the box for Hynes, but Price blocked his effort.
Rovers started the game well but their only effort in the first half came in the third minute when Robert Bayly hit the post.
Longford Town -- Shanahan, O'Reilly, Lester, Deans, Lee, Freeman (Brady 76), Salmon, Hyland, A Roche (Cronin 86), Hynes, L Roche (Oladele 73).
Shamrock Rovers -- Mannus, Chambers, Sives, Price, Stevens, Kavanagh, Bayly (Rice 68), Turner (Bradley 60), Dennehy, Twigg, Fenn (McGuinness 76).
Ref -- R Winters.