Blackrock have qualified for their first Cork SHC final since 2003 but they must wait to find out who their opponents will be as Sarsfields and Imokilly finished all square.
The Rockies timed their run to perfection to get the better of Na Piarsaigh by 0-21 to 2-14.
With Michael O'Halloran top scoring with 0-8 (six from frees), they outscored their opponents by six points to one in the final quarter.
Sarsfields, meanwhile, were held to a draw after Paudie O'Sullivan sent over a 64th minute equaliser for Imokilly.
The Pairc Ui Chaoimh scoreboard read Imokilly 1-24 Sarsfields 2-21 at the final whistle.
Cian Fleming registered 1-5 for the East Cork Division while Jack O'Connor and Tadhg Og Murphy's accounted for Sarsfields' goals.