Before his passionate home crowd at the Cardiff Ice rink, Robinson displayed composure, speed and intelligence to break Murphy's resistance in the ninth round. The St Albans boxer, who had been under pressure throughout, finally wilted under a blistering two-fisted barrage.
On one knee, he made a valiant attempt to rise but misjudged the count and was officially stopped after 1min 40sec of the round by the referee, Roy Francis.
Robinson thus retains the title he won last April when he defeated John Davison, a contest he had taken at just 48-hours notice. On this evidence, the former storeman's reign may be considerably lengthier than many experts had predicted.
Murphy fought his usual fight, pressing forward relentlessly looking to break his rival's heart under a sustained volume of punches. Robinson however, maintained his composure, switching his attack cleverly from head to body.
As early as the fifth round there were signs that the challenger was in trouble. In the sixth, Murphy walked on to a straight left but as one of the most durable and bravest fighters in British boxing he continued to attack.
Robinson's attack continued with the same mixture of body shots, left hooks and fast combinations until the challenger could finally take no more. Sitting at ringside was Colin McMillan, the former title-holder, who may now be Robinson's next opponent.
PROFESSIONAL PROMOTION (Cardiff): 12- rd featherweight (for WBO Championship): S Robinson (Cardiff, holder) bt S Murphy (St Albans) ko 9th. 6-rd cruiserweight: C Okoh (Croydon) bt S Yorath (Cardiff) pts. 8-rd super- middleweight: N Piper (Cardiff) bt T Ambrose (Leicester) rsf 5th. 6-rd super-featherweight: N Haddock (Llanelli) bt A Levine (Liverpool) rsf 5th.