The striker drilled home from close range in the 19th minute as we beat Pompey 1-0 at Havant & Waterlooville's Westleigh Stadium.
Runners-up spot had already been secured in Barclays Premier Reserve League South and Clive Allen's squad completed the season with seven wins in their last eight games.
FULL-TIME: POMPEY 0, SPURS 1
83.31: SAVE - BEGOVIC. Mtandari found a gap with a curler from 16 yards that Begovic clutched diving to his left.
79.50: WOODWORK - SPURS. Hutton sent Mtandari away down the left, cross deceived Begovic and clipped the top of the crossbar.
60.40: SAVE - BEGOVIC. Livermore and Hutton opened it up for Maghoma to spin and shoot from 15 yards, good reactions from the keeper to palm away diving to his right.
46.50: CHANCE - SPURS. Hughton into Maghoma, right side, clear sight of goal but drilled just wide.
3.33pm: Second half has kicked-off.
HALF-TIME: POMPEY 0, SPURS 1
43.30: SAVE - BEGOVIC. Good feet from Kasim on the edge of the box before a reverse pass set up Fraser-Allen, right side, good hit but Begovic got his angles right and parried away at near post.
33.01: CHANCES - POMPEY. Good chances but fantastic defending. Traore's cross from the left initially drilled at goal by Cuvelier, blocked by Gilberto and the follow up from Nlundulu blocked by Mtandari - both efforts from 12 yards. Kilby then hammered wide from the edge of the box.
31.55: SAVE - BEGOVIC. Hutton sent Dawkins away down the left, low cross went all the way through to Kasim at the far post, Begovic got across his line to block side-foot at foot of the post.
18.55: GOAL - SPURS. Maghoma picked pass in tight space to Kasim, edge of the box, he worked a yard of space before letting fly, shot blocked but ball fell to Dawkins who rammed home from six yards.
Pompey 0, Spurs 1
4.28: OFF LINE - SPURS. Dawkins sent Fraser-Allen away through the middle, skipped around Begovic, rolled ball towards goal from tight angle but Sowah back to clear. Play continued, Hutton picked out Kasim at the far post, volleyed wide.
2.31pm: We've kicked-off at Westleigh Park.
Pompey: Begovic, Mantyla, Sowah, Pack, Woodford, Wilkinson, Nlundulu, Cuvelier, Gazet du Chatelier (Alors, 46), Kilby, Traore (Smith, 46). Subs: Stewart (GK), Martin, Goddard.
Spurs: Alnwick, Hughton, Gilberto, Livermore, Rocha, Mtandari, Fraser-Allen, Maghoma, Dawkins, Kasim, Hutton. Subs: L Butcher (GK), Smith, Nicholson, Ekim, Cox.