Fry bacon in large skillet over medium-high heat until crisp, about 5 minutes. Transfer bacon with slotted spoon to plate lined with paper towels. Spoon off all but 2 tablespoons bacon fat.
Meanwhile, place flour in shallow dish. Season chicken with salt and pepper, dredge in flour, and shake to remove excess. Add butter to reserved bacon fat in skillet and heat over high heat, swirling to melt butter. When foam subsides, reduce heat to medium-high and cook chicken until browned on both sides, 3 to 4 minutes per side. Transfer chicken to plate (leaving fat in skillet) and cover loosely with foil.
Reduce heat to medium and add garlic, rosemary and pepper flakes. Cook until garlic is browned and crisp, about 2 minutes. Add broth and lemon juice, scrape up browned bits from bottom of skillet with wooden spoon and simmer until slightly thickened, about 4 minutes.
Return chicken and bacon to pan and simmer, turning chicken once or twice, until sauce is thick and glossy, 2 to 3 minutes. Adjust seasonings and serve immediately.