Facing a superior pack, led by southern hard men Jason Rutledge and Jamie Mackintosh, the Steelers negated Southland's muscle by holding onto the ball for a 70 percent share of the possession.
With that possession, Counties caused havoc with its lethal back line that built on the confidence and form from two pre-season victories - against Waikato and Taranaki.
The visitors struggled to find inspiration on a special night for Rutledge and Gloucester-bound Jimmy Cowan. The former became the most capped Southland player in history but also gave away a game-changing try that the home side would not give back.
The Steelers were without inspirational captain DJ Forbes who injured a shoulder during a New Zealand sevens training camp, while Southland were forced to make do without flanker John Hardie (toe).
Counties capitalized on a dominant opening period, where they made a strong statement running with ball in hand from their own 22.
Advancing steadily into opposition territory, Kerr opened the Steelers' account with a penalty in the sixth minute after Sherwin Stowers was denied the opening try by referee Nick Briant.
Five minutes later, 23-year-old Kerr orchestrated another scoring play when his offload in close quarters put Fritz Lee through to score next to the posts.
The early pace set by Counties began to take a toll on the tiring Southland line.
For the visitors, it was always going to be about their men up front - whose tight running managed to slow the pace of play then earn a penalty which first-five Scott Eade converted to close the gap to seven.
A dominant Steelers scrum drew a penalty in the dying minutes of the opening spell. After electing to pack down once again, Fritz Lee finished off a sniping run by halfback August Pulu with his second five-pointer of the match.
Kerr's conversion sent the home side into half-time with a nine-point cushion.
After the break, Counties invited pressure immediately with a misfired pass inside the 22, which lead to a penalty that Eade used to reduce the deficit by three.
In his milestone game for the Stags, Rutledge would have been embarrassed by his cameo in the backline when he delivered the ball into the hands of Steelers prop Simon Lemalu. The 118kg front-rower showed a clean pair of heels while running 20 metres to score in the corner.
Facing a 16-point deficit, ill-discipline crept into the Stags' play and the penalty count- once firmly in the visitors' favour - began to equalise.
Despite numerous opportunities to firmly 'shut the door' on their Southern counterparts, Counties lacked the patience and composure needed to deliver the final blow.
Desperately searching for a bonus point, second-five Aki set the field alight with his 50-metre solo effort to score within inches of the corner post.
Counties-Manuakau 30 (Fritz Lee 2, Simon Lemalu, Bundee Aki tries; Bayden Kerr 2 con, 2 pen)
Southland 9 (Scott Eade 3 pen)