Since the turn of the century the two sides have only played each other on 10 occasions, and during the entire 1990s they only met once in the FA Cup.
There were only three derbies during the 1980s and in the 1970s they played four times – and in total the two clubs have only met 72 times in 125 years.
“The last derby was in 2019, and that was a long time for the grudge to be held,” added Farmery.
“There’s a lot of build-up over a long period of time and because that boil doesn’t get the chance to be lanced often enough, that contributes to the ferociousness of the rivalry.”
Southampton club historian Duncan Holley believes the fact that Saints have traditionally finished higher in the football pyramid has also fuelled the rivalry.
“In the past 64 seasons, Saints have only been below Portsmouth in finishing terms on seven occasions,” he said.
Holley said that relative success annoyed Portsmouth fans and “by the time the 1960s ended there was a lot of animosity coming from Portsmouth to Southampton”.
He added: “Saints fans then retaliated and decided to match the feeling, and that’s how it all became.
“There is always rivalry between any neighbouring town, and this was initially a friendly competitiveness, but that really petered out. It’s become a bit of a cult and I see it as one of the strongest derbies around.”