Pat duck breasts dry with paper towels. With sharp knife, cut 4 diagonal slashes, about 1/4 inch deep, in skin and fat on each breast half. On sheet of waxed paper, evenly season duck breasts, on both sides, with 1/4 teaspoon salt and 1/8 teaspoon coarsely ground black pepper.
In 12-inch nonstick skillet, cook breasts, skin side down, on medium 15 minutes or until skin is well browned and crispy. As breasts cook, spoon off and discard fat in skillet. Turn breasts over and cook on flesh side about 4 minutes for medium-rare or until desired doneness. Transfer breasts to cutting board; cover with foil to keep warm until ready to serve.
Discard all but 1 teaspoon duck fat from skillet. Add shallot and cook on medium 2 to 3 minutes or until beginning to brown. Stir in garlic and cook 1 minute. Add port wine, balsamic vinegar, and cherries; heat to boiling. Boil 3 minutes or until sauce is reduced to 3/4 cup, stirring frequently.
To serve, thinly slice each breast and transfer to a dinner plate. Spoon port sauce over breasts.