After many mistakes I made, I think I will never get confused with "a" and " the". But sometimes, sentences written by native-speaker really baffle me.
Here is the sentence taken from theguardian.com link.
Guardiola’s infringement came after Raheem Sterling’s injury-time goal gave City a 2-1 victory at the Etihad on Wednesday.
The author writes " a 2-1 victory". Why is that? Why not " the 2-1 victory"? City beat Southampton 3 days ago so "2-1 victory" is already specific, right?