The 27 year-old took every round of seven from the Filipino challenger until a cut opened up by a clash of heads earlier in the fight was deemed too bad to continue the contest.
There was never any doubt who would get the decision as the judges’ cards read 70-63 across the board in favour of the champion.
Experienced campaigner Sor Singyu moves his record to an impressive 52-3 with his latest triumph, whilst southpaw Pabustan drops to 26-3-6 and heads back to the drawing board.
Sor Singyu had taken three attempts to finally land the WBO belt at 118lbs having originally lost to Paulus Ambunda and Tomoki Kameda in previous challenges.
Finally, the Thai star claimed his first recognised title with a second round stoppage of Ryo Akaho last August, and on recent form, could be set for a long reign as a WBO divisional ruler.