Pompey had failed to win any of their past five meetings with Plymouth.
But Kal Naismith’s first half finish – following a mistake from goalkeeper Remi Matthews – saw them come out on top at Fratton Park.
Three of those previous clashes had finished all square and all of them were extremely close contests.
So Brandon Haunstrup was delighted that the Blues were able to hold on to their slender lead to secure the points.
The left-back said: “We always seem to have tight matches against them and it was no different on this occasion.
“The last 10 minutes did see us come under a bit of pressure, but that was only to be expected in the circumstances.
"This match is one that probably gets talked about a bit more than others among the fans, but we just treated it as another game."
“That ability to see games out when you’re ahead is something we’ve needed to be better at – and we’ve worked on it.
“The long throw into the box is one of their strengths, although I felt that we dealt with it well in the end.
“This match is one that probably gets talked about a bit more than others among the fans, but we just treated it as another game and were able to come out on top.”
It was an impressive performance from Haunstrup, who managed to keep arguably Argyle’s s biggest threat quiet.
He said: “We knew that Graham Carey was one of their better players and wanted to keep him back as much as we possibly could.
“I just had to keep as tight to him as possible and he didn’t really get at me in the second half, while they didn’t feed him that much.
“We dealt with him really well and I suppose it’s always a good sign when your opponent gets taken off.”