Just before halftime, Nick Land won the ball at halfway, advanced up the left and squared the ball to Somerton, who tucked it into the near-post corner of the goal for a 2-0 halftime lead.
Peringa got one back in the 57th minute, in unusual circumstances. A long-distance shot hit the underside of the bar, and the ball bounced down and out. Play continued for about half a minute until a break in play, when the referee asked the assistant referee whether the ball had crossed the goal-line. She said it had, and the goal was awarded.
Thistle regained a two-goal cushion in the 81st minute. Xavier Priestley played the ball to Gavin Derr, who advanced up the left wing and passed inside to Samson Hotas.
His shot was blocked but he volleyed the rebound past the keeper from six metres.
Somerton brought up his hat-trick in the 88th minute, going past a defender on a run up the left wing and firing a shot into the far corner of the goal.
Thistle coach Tam Cramer said it was a good team performance.
They had Hugo Lodewyk in goal, Wirepa-Hei at right back, Shai Avni at left back, and Junior Jimmy and Ziggy West-Hill as dual centre backs. The central midfield was Euan Cramer, Land and Cory Thomson, with Hotas on the right flank and Kaden Manderson on the left. Somerton was up front.
Priestley and Derr came on for Cramer and Manderson respectively midway through the second half.
Thistle have two Federation League games to play and need a win to ensure they retain sixth place. They have no chance of overhauling Havelock North Wanderers, who are seven points ahead on 25, but New Plymouth Rangers are close behind, on 16.
Rangers have one game to play, against last-placed Peringa.
Thistle’s games are against fourth-placed Taradale and fifth-placed Havelock North.
Meanwhile, Heavy Equipment Services Gisborne United won the Eastern League Bailey Cup men’s knockout final at Harry Barker Reserve on Saturday.
United, the Eastern League 1 champions, beat Smash Palace Shockers Gold 4-2.
