Portsmouth Under-18s 1 Argyle 2
League leaders Pompey suffered their first defeat of the season as the young Pilgrims travelled home with all three points after recording their fifth straight victory.
Goals from Alex Fletcher and Jason Vincent gave Argyle's fledglings yet another victory in this excellent run of form.
The scorching hot conditions did not help the Argyle squad as many of them had played 120 minutes in last Tuesday's under-21 Premier Cup victory at Home Park.
After enjoying the better of the first half exchanges it was the home side who got stronger as the second half wore on and only three fine saves from Michael Cooper kept the Greens in the game until substitute Jason Vincent grabbed his late winner.
Argyle ran the first half with Alex Fletcher firing across goal before the home 'keeper required two attempts to save Jack Calver's fiercely struck free kick. Jake Miller and Luke Jephcott had seen goalbound efforts deflected wide before the interval arrived with the game goalless.
It took Pompey just two minutes of the second half to open the scoring but Argyle were level two minutes later.
Fletcher intercepted a central defender's pass to run in to the area and supply a cool finish past the advancing Pompey 'keeper.
Cooper then made three fine saves while Liam Knowles and Jordan Bentley got in last-gasp challenges to keep the scoreline level before Calver's 85th minute corner found substitute Vincent heading in to the far corner of the home goal for the winner.
Argyle: Michael Cooper, Billy Palfrey, Jordan Bentley, Owen Jones, Liam Knowles, Dan Rooney, Jake Miller, Jack Calver, Alex Fletcher, Alex Battle, Luke Jephcott (Jason Vincent 75).