It depends who you talk to, but I think there's some logic in saying that a clause is simply another name for a verb phrase. (Ignoring non-verbal clauses.) Two verbs mean two clauses.
Infinitive arguments can have their own set of independent arguments and adjuncts. Here is a complex example, but I think it illustrates that there are two clauses quite clearly:
Last night at the bus stop the son
wished for the father
to read a story to him in bed when they next went to grandma's house.
Two locative adjuncts: at the bus stop and in bed
Two temporal adjuncts: Last night and when they next went to grandma's house
Two subject arguments: the son and the father
And the infinitive verb has its own set of object arguments which are not arguments of wish: a story and him
Strip all that back and you get
The son wished to read.
Rather than propose that it has a different structure I think it's best to say that it has the same structure: two clauses.