In Collier's story, the imaginary friend belongs to a young boy rather than a grown man. But the major difference between the two is that Chase's play is a comedy, while Collier's is definitely not.
While I was once again engaged with this story, I did find the dialogue odd. Granted some may have been intentional (there's a windbag of a father who likes to spout his superior knowledge of child-rearing), others may have been due to the time and place the story was written (England, 1940s). (Though I have to admit, it made me envision Jeff Goldblum in the role.)
Despite that, I liked the pacing of the story and buildup of danger. What begins as a generic childhood scene of a boy playing with an imaginary friend, escalates into a power-struggle between the boy and his dad-- but still, at this point, not an uncommon scene. Then it gets ugly.