Substitute Latifi capped a run along the left with a decisive finish to increase the Orchard County lead to 3-1.
Argyle cut the gap but County Armagh managed to protect the advantage for a 3-2 success.
Alberto Balde added to his tournament tally with the opening goal inside the first 15 minutes.
Argyle’s set-piece strength led to an equaliser and the game’s final goal - with County Armagh adding to the Junior Section lead thanks to Chris Hutchinson.
“We were aware of Plymouth’s strengths and set up a gameplan to try and counter that technical ability and width,” said County Armagh coach Dean McCullough. “Our goal was to grab the lead and it worked out well in terms of moving 1-0 up early on.
“We were under pressure at stages but it would have been an injustice not to get a win after our performance.”
JUNIOR SQUAD: Adam McAlpine (Glenavon), Daniel Gordon (Portadown Youth), Jack Adamson (Portadown Youth), Lee Upton (Portadown Youth), Jack McIvor (Glenavon), Patrick Kerr (Armagh City), Rioghan Crawford (Lurgan Celtic), Scott McCann (Loughgall Youth), Chris Hutchinson (Portadown Youth), Alberto Balde (Portadown Youth), Ryan Carmichael (Loughgall Youth). SUBS (used): Ryan Latifi (Portadown Youth), Tom Barratt (Portadown Youth).