Hello Anon
The "subject complement" is a word or phrase that tells us more about the subject, e.g.
1. MrQ is a very strange fellow.
2. Juventus are top of the Italian football league.
The underlined portion tells us more about MrQ in the first example, and Juventus in the second.
Your examples aren't subject complements – they're statements (in the declarative mood). You could call the underlined portion a predicate, however, e.g. in your first sentence:
3. John bought the tickets.
MrP