Main files about penultimate game (9)

I believe the answer is:

semifinal

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for semifinal that I've seen before include "late stage in contest" , "Penultimate round of a competition" , "Competitive match" , "big match" , "Tie" .)

I've seen this clue in The Daily Express.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.