Southern fell to its first loss of the season to a determined Pirates side at Bathgate Park.
Ahead 7-3 at the break, Pirates defended stoutly against a rather one-dimensional Southern unit, and then took their chances when they came along.
Pirates first five-eighth Glenn Dickson, having just arrived back from playing in England, and a few days in Australia, used his big boot to good effect and kicked a crucial sideline conversion near the end to put Pirates ahead.
He also scored the first try of the day when he picked up a dropped Southern ball and ran 30m to score.
The Pirates line-out competed well against a Southern side, which spilled too much ball.
Southern also tended to keep the ball too close in and that was meat and drink for the Pirates defence.
Pirates centre Marshall Suckling ran hard while halfback Steve Bruce fed his backline well.
Up front, flanker Josh Clarke got through plenty of work, and lock Nic Wilson got round the paddockBest for Southern were halfback Harry Uffindell and lock James Stevenson.
Pirates 17 (Marshall Suckling, Glenn Dickson tries; Dickson 2 conversions, penalty goal), Southern 13 (Carl Anderson, Warren Moffat tries; Julius Glasson penalty goal).
Halftime: Pirates 7-3.
Referee: Ross Barnett.
