I agree that comical and humorous are pretty much synonymous, but I think you can have both "comic" and "comical". A comic play and a tragic play are actually two archetypes of drama. A comic play may not necessarily be comical/humorous, but it follows a certain formula.
To me, the difference is a point of view. A comic love story may be intended to be humorous, but I may not personally find it humorous. In other words, it may be intended to get a laugh but doesn't get one from me.
If someone says "a humorous love story", I assume they found it funny. If they say, "a comic love story", I know what the intentions of the playwright were but not the opinion of the person speaking.
I had to translate 'comercial humorístico', I went with 'humorous commercial', since the idea was to sell the comercial itself. In a more impartial type of writing, then I would've chosen 'comic comercial'. Would you say that's correct? Any thoughts or suggestions?