The dominant Southern pack got the better of Taieri and paved the way for a win in a niggly game at Bathgate Park.
The powerful front row of Warren Moffat, Ean Griffiths and Kees Meeuws gave the Magpies the advantage in the scrum.
Blindside flanker Sam Crompton did his job at the breakdown and dynamic No 8 Andrew Stead was difficult to stop with the ball in hand.
Taieri had opportunities to attack but was not able to breach the defensive shield spearheaded by the midfield of Luke Herden and Nick Jones.
Herden's ability to stand in the tackle after the half break created opportunities for speedy wings Joe Hill and Seb Hill.
Tries to Joe Hill and Andrew Stead gave Southern a 13-6 lead at the break and two more tries were added in the second spell.
A Herden break midway through the spell led to Seb Hill's try and the game was taken out of Taieri's grasp when lock Tom Franklin scored the bonus-point try.
First five-eighth Andrew Reid kicked three penalty goals for Taieri and loose forwards Charlie O'Connell and Nathan Young had strong games at the breakdown.
- Southern 25 (Joe Hill, Seb Hill, Andrew Stead, Tom Franklin tries; Robbie Smith con, pen), Taieri 9 (Andrew Reid 3 pen). Halftime: Southern 13-6.