Daisy Fuentes & Duffy -- Show Major Mutt Mercy ... Save Dog From Death

Animal shelters should keep Grammy winning singer Duffy and Daisy Fuentes on speed dial ... because together they're a one-two dog saving punch.

Our doggie sources say Duffy caught wind through an online dog forum that Bronx -- an adorable American Bulldog -- had one hour to live before an Orange County adoption center put him down ... so she stepped up and slipped $1,000 to L.A. shelter, Ace of Hearts to save him.

That's when Daisy got involved. We're told she was looking to foster a pooch and fell in love when she met Bronx at Ace of Hearts. Bronx is now shacking up with Daisy ... who's covering all the costs to get him ready for adoption -- and that includes potty training.

Such good girls ... yes you are.