Daire Rowe's eight and final point proved the difference between the sides in this closely-fought IFC opener at Bective.
Rowe shot the winning score from a free in the 55th minute after the sides were level on six previous occasions in the second half.
County player Mickey Burke had a chance of an equaliser for Longwood when he found himself unmarked in the final minute but he pulled his shot wide of the target.
Referee Dessie Smyth issued three red cards in that second half. Syddan sub Luke Halpenny and Longwood full back Enda Dixon were sent off five minutes from the finish while Longwood sub Coran Byrne received his marching orders in added time.
Evan Coyle had the games' opening score for Longwood but Syddan took control for a spell after that during which they hit a goal and four points.
The goal came on seven minutes when Daire Rowe and Thomas Dillon combined to set up Ronan Mooney who shot low to the net.
Longwood got back into the match when Ryan Moore had a simple tap in for a goal following an error in the Syddan rearguard on 16 minutes.
Syddan then lost Paddy Farrelly to a black card as Longwood closed the deficit to two points by half-time, 1-6 to 1-4.
The village side were level following points from Burke and Moore within three minutes of the restart and Longwood led for only the second time when Moore converted a free on 38 minutes.
It was point for point after that with Syddan leading twice following efforts from Kevin Traynor and Rowe.
However it was Rowe who had the final say to give last years quarter finalists a winning start.
SYDDAN - Kieran Farrelly; Mark Fedigan, Jack Reid, Kevin Garland; Andrew Garland, Kevin Traynor 0-1, Ian Curran; Sean Clare, Stephen Dillon 0-1; Paddy Farrelly, Ronan Mooney 1-0, Cormac Rowe; Gary Farrelly 0-1f, Thomas Dillon, Daire Rowe 0-8 (5f). Subs - James Farrelly for P Farrelly (BC 18), G Garland for A Garland (43), Luke Halpenny 0-1 for T Dillon (47).