On the pitch, there's a fascinating battle ensuing between Pompey and their League One rivals for promotion back to the Championship.
But that rivalry is not confined to the field of play, with supporters from the third tier also vying for top spot when it comes to best away attendances.
Another 1,500-plus Pompey crowd is expected at Carlisle United tomorrow. Meanwhile, the Blues have sold out their 2,000-plus ticket allocation for next month's trip to Blackpool.
That represents fantastic loyalty, but how does it compare to what the rest of the clubs in League One have to offer when it comes to away-day support?
Well, we've got our calculator out to find out - and here's what her discovered...
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