In a prime position in the Spanish Open for one hour (8)
I believe the answer is:
eleventh
'in a prime position' is the definition.
(11 is a prime number)
'the spanish open for one hour' is the wordplay.
'the spanish' becomes 'el' ('the' in Spanish).
'open for one' becomes 'event' (open is a kind of event).
'hour' becomes 'h' (abbreviation).
'el'+'event'+'h'='ELEVENTH'
'in' is the link.
(Other definitions for eleventh that I've seen before include "This hour offers the last chance" , "Next after tenth" , "at such a late hour?" , "last man in?" , "it's after ten" .)