Stir the soup, sugar, lemon juice, oil, Worcestershire, garlic powder and thyme in a medium bowl.
Lightly oil the grill rack and heat the grill to medium. Grill the steak for 10 minutes for medium-rare or until desired doneness, turning the steak over halfway through cooking and brushing it often with some of the soup mixture. Let it stand for 10 minutes before slicing.
Pour the remaining soup mixture into a 1-quart saucepan. Heat over medium-high heat to a boil. Serve the sauce with the steak.
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