Quote:The author probably wanted to say, China is one of the few countries which have sent men into space.
That is right. The use of "only" in this way is correct. It is used to direct attention to the small number of countries (two) which had previously sent a person into space. It is a term of praise therefore. It does not mean that China has performed poorly in a race. Of course being first is notable, but when discussing such a difficult achievement, being second or third is still worthy of mention. Consider the following...
John Smith (
ficticious example) was only the third English person to climb Mount Everest.
At just 48 years old and not even nine months in office, Obama became only the third sitting U.S. president to win the Nobel Peace Prize.
Paul McCartney was only the third artist to win the Gershwin Prize For Popular Song.
Makhaya Ntini was the first ethnically black player to play for the South African team and only the third South African to take 300 Test wickets.
Quote:So, if I say "the third only country...", am I right?
No, you cannot use "only" like that.