Rathdowney-Errill emerged from the championship opener as nine point winners.
The defending Laois hurling champions have suffered an early set-back.
A meeting of Camross and Rathdowney-Errill promised much before the off and delivered more.
Poor playing conditions didn't prevent entertainment flowing with seven goals and 35 points shared between the two sides.
Camross never fully recovered from a slow start, trailing by six at the break, meaning last year's beaten semi-finalists claimed an early scalp on a final scoreline of 4-21 to 3-14.
In the championship's other group, The Harps face Rosenallis at the LOETB in Portlaoise, while tomorrow Portlaoise and Castletown meet at the same venue.
Both games throw in at 7.30pm.
Sallins Prove Too Strong For Tubberclair In Leinster Decider
Portlaoise Panthers Suffer Defeat In Women's Super League
Leinster Overcome Leicester Tigers With Strong Second Half Performance
Medals Secured For Ireland At European Cross Country Championships
All Ireland Glory Achieved By Camross
Dublin Lions End Portlaoise Panthers' Perfect Home Record
Success For Camross But Heartbreak For Tubberclair
Portlaoise Panthers Back In Super League Action This Weekend
Camross Name Tomas Burke As New Hurling Manager
Midlands Stars Set For European Cross Country Championships
Laois U20 Hurler And Footballer Of The Year Revealed
Camross Has Nothing To Lose This Weekend - Arien Delaney
Robbie Henshaw Named To Start For Leinster's Champions Cup Clash
Leinster Glory The Target For Tubberclair This Weekend
Portlaoise Panthers Aiming To End Losing Streak
Camross Getting Set For All Ireland Final
Westmeath Boxers Set To Compete At U17 European Championships
Portlaoise Panthers U20s Seal Semi-Final Place In National Cup
Midlands Beko Club Champions Recognised At Croke Park
CCFL: Four Teams Progress In Combined Counties Shield