In a cagey contest, that ultimately failed to ignite, Parker took the fight 115-113 on two of the judges’ cards after the completion of twelve rounds.
The early exchanges were all Ruiz as Parker looked a tad nervous, although the home fighter soon settled into the bout and begun racking up points.
Ruiz managed to find a second wind into the final five rounds and heading into the eleventh the WBN scorecard saw the clash dead level at 95-95.
For me, Ruiz came on a little stronger to take the last two sessions but the judges saw it different as the Mexican-American suffered his first career loss.
In the end, a final ringside scorer had the encounter 114-114 as Parker moved on to a first defence of the title, possibly against Hughie Fury in the spring of 2017.
Also on the bill at the Vector Arena in Auckland, super bantamweight Isaac Dogboe pushed to 16-0 with a seventh round stoppage of Julian Aristule, whilst welterweight Jeff Horn halted Ali Funeka in six to continue his rise up the rankings.
Junior Fa, Shannon O’Connell, David Letele and John Parker, brother of headliner Joseph, picked up a second win at the cruiserweight limit over four rounds.