In a medium bowl, stir together the olive oil, bottled ranch dressing, Worcestershire sauce, dried rosemary, salt, lemon juice, white vinegar, ground black pepper, and white sugar. Let stand for 5 minutes.
Pound chicken breast to 1/4 inch thickness.
Place chicken in a gallon-size ziplock bag, and stir to coat with the marinade. Cover and refrigerate for a few hours to overnight.
Preheat the grill for medium-high heat.
Grill chicken for 8 to 12 minutes, or until the chicken is no longer pink in the center, and the juices run clear.
