Denied the US Open championship trophy, Leylah Fernandez decided to make off with the spotlight instead. Visibly exhausted, her face both beaming and wet with tears, the 19-year-old Montreal native — bested in Saturday’s women’s final in straight sets, 6-4, 6-3, by an even younger British tennis darling — refused to say goodbye to Flushing Meadows. Rather: until next time.