It was courtesy of some slick work from Symons, which laid on Tasman's first try as his well-timed pass found Lowe who showed plenty of gas to fly down the touchline and dive over the chalk in the 18th minute.
Earlier, Tasman were forced in to a backline reshuffle when five-eighth Hayden Cripps was a late scratching, which saw veteran utility Robbie Malneek called upon to run the cutter but he didn't see out the first half.
Malneek was plagued by a hamstring issue and was forced off in the opening spell and was replaced by debutant Billy Guyton.
Symons' and Guyton's accurate goal-kicking provided Tasman's other points as they took a 14-6 lead with them to the half-time break.
Southland, who barely fired a shot in the opening spell, were forced to rely on two penalties from Scott Eade as their only source of points.
Eade then added the first points of the second spell as he stroked another penalty through the uprights in the 46th minute as Southland inched back in to the contest.
Tasman's versatile lineout proved a good source of clean ball during the encounter as it operated with an impressive efficiency.
Southland flanker John Hardie had a busy evening at the office as he tore around the paddock and got involved regularly.
Eade added another penalty in the 50th minute as the home crowd began to find their voice as they moved to within two points at 14-12.
But Guyton restored Tasman's five-point advantage with a penalty goal of his own as the game meandered along during the middle of the second spell.
Guyton then booted three more points and after Lowe's second, Tasman secured a valuable victory on the road.
Tasman 25 (James Lowe 2 tries; Andrew Symons 2 pen; Billy Guyton 3 pen) Southland 15 (Scott Eade 5 pen) HT: 14-6
