4 tablespoons (1/2 stick) butter
1 1 1/2-pound top sirloin steak (about 1 inch thick)

1 large onion, chopped
3 large garlic cloves, chopped
1/2 cup bottled chili sauce
2 tablespoons Worcestershire sauce
2 tablespoons fresh lemon juice
2 tablespoons (packed) dark brown sugar

Melt 1 tablespoon butter in heavy large skillet over medium-high heat. Sprinkle steak with salt and pepper. Add steak to skillet and saut to desired doneness, about 4 minutes per side for medium-rare. Transfer steak to cutting board.

Melt remaining 3 tablespoons butter in same skillet over medium-high heat. Add onion and garlic; saut until tender, about 8 minutes. Add chili sauce, Worcestershire sauce, lemon juice and brown sugar. Simmer 3 minutes to blend flavors, stirring occasionally. Season sauce to taste with salt and pepper.

Slice steak thinly. Arrange on platter. Spoon some sauce over. Serve, passing remaining sauce separately.