Bring a large pot of water to a boil; salt generously. Add spaghetti, and cook until slightly underdone, about 7 minutes. Drain pasta, reserving 1 cup of cooking liquid. Set aside.
Meanwhile, heat oil in a large skillet over medium heat. Add garlic and chile pepper; cook until garlic is golden, about 2 minutes. Add clams and white wine, and raise heat to high. Bring to a boil; cover, and cook, shaking occasionally, 2 to 3 minutes, until clams open. Stir in parsley. Transfer to a bowl; set aside.
Return skillet to medium-high heat. Add reserved pasta water and lemon juice; reduce until slightly thickened, about 2 minutes. Remove from heat; whisk in butter. Add clam mixture and spaghetti. Cook over medium-low heat until heated through, 2 to 3 minutes. Season with salt and pepper; garnish with parsley.