Inspired by the three McLoughlin brothers, Blessington were full value for their 1-13 to 0-4 win, with midfielder Anthony McLoughlin chipping in with 1-2 and centre-back Paul adding a point.
The Saints will be bitterly disappointed with their display, never got out of the starting blocks and trailed by 0-6 to 0-4 at half time.
Baltinglass goalkeeper John Flynn fired over the winning point in their opening round clash with arch-rivals Rathnew.
Early in the first half, Flynn twice came off his line to deal with Rathnew frees but full-forward Mark Doyle beat him and full-back Tommy Murphy to punch two rapid fire goals, giving Rathnew a 2-1 to 0-1 lead after six minutes.
Baltinglass clawed their way back into the match, reducing the deficit to 2-3 to 0-6 at the break.
With the game deadlocked at 2-8 to 0-14 on 60 minutes, Flynn showed nerves of steel as he drilled a 50m effort between the posts.
Super-subs Nick Skelton and Conor Flannery did the trick for Carnew and Bray Emmets in their respective first round games on Saturday at Aughrim.
Skelton came off the bench to score the winner for Carnew as Kiltegan fought their way back to parity after Carnew wing-back Mark Collins had given his team a 1-7 to 0-7 lead with a goal ten minutes into the second-half.
County star Seanie Furlong rediscovered his form after Wicklow’s disaster against Armagh to score all but two of Kiltegan’s 0-11, but it was not enough to stop them going into the qualifiers when Skelton grabbed the winner for Carnew (1-9 to 0-11) in injury-time.
Conor Flannery was only minutes on the field when he scored Bray’s final brace of points, one from a free, that gave them a narrow 1-6 to 0-8 win over Arklow Geraldines Ballymoney.
The final result of the weekend will cause headaches for fixtures boss Mick Hagan after St Mary’s and Annacurra drew 2-10 to 1-13. Annacurra led by three points at half time. St Mary’s goals were scored by Don Jackman and Conor Walker while Martin O’Brien scored a cracker for Annacurra.