Little blue Smurfs and not-so-little green men from space are in a photo finish for the No. 1 spot at the weekend box office. According to studio estimates Sunday, Daniel Craig and Harrison Ford’s sci-fi Western “Cowboys & Aliens” and the animated family adventure “The Smurfs” both opened with $36.2 million. That leaves Sony’s “Smurfs” and Universal’s “Cowboys & Aliens” tied for the top spot. Actual weekend rankings won’t be sorted out until final numbers are counted Monday.