Howley pinched the ball from the Scarlets, chasing an equalising try, on his own 22 and set off, knees pumping, on a headlong dash to the corner which Wayne Proctor was unable to cut off. If ever a player should be wrapped in the proverbial cotton wool - or should that be Fran Cotton's wool - before the Lions tour, it is Howley.
Here he was absolutely on top of his game, and what a game he has. Head up, alive to every situation, Howley snaffled two quick-witted tries in the first half and, Cotton may or may not wish to note, shunned any involvement in the sporadic dust-ups.
Howley's eclipse of Rupert Moon was not quite total - the Llanelli scrum- half's try from a short penalty in the 62nd minute sparked a surging last quarter from the Scarlets.
But Llanelli had left themselves too much to do, looking anything but the form team in Wales, let alone the team which had won both this season's league meetings between the clubs.
The absence if Ieuan Evans, scorer of 48 cup tries down the years, with a calf injury, did not help. But the vital exchanges were, of course, up front. When Derwyn Jones was not putting himself about on the wrong side of rucks, he put in some valuable line-out work for Cardiff.
And the ferocious tackling and ball-retrieval of Mark Bennett made light of the injuries which deprived Cardiff from the start of back-row caps Hemi Taylor, Emyr Lewis and Gwyn Jones.
At 28-9 down at the break, Llanelli seemed dead and buried. Their best hope lay in Frano Botica's instincts for keeping the ball alive.
Llanelli's frantic attacking efforts in the latter stages paid their first dividends with Moon's try then a penalty by Botica, whose quality goal-kicking duel with Lee Jarvis was nevertheless reduced to a sub-plot.
Taylor, not quite a fresh pair of legs, put his troublesome hamstring to the test when he replaced Bennett and Cardiff also sent on Lee Jones in a damage limitation exercise which was aided by Jarvis' long-range penalty goal.
If that success, Jarvis's sixth from seven attempts, steadied Cardiff's nerves, their vulnerability to the short penalty move did not. Llanelli centre Nigel Davies cut through for his side's second try and Botica's conversion raised the decibel level among the Scarlets' followers to new heights. But Howley had other ideas, and too many of them for Llanelli.
Llanelli: Tries Moon, N Davies; Conversions: Botica 2; Penalties Botica 4. Cardiff: Tries Walker, Howley 3; Conversions Jarvis 2; Penalties Jarvis 4.
Llanelli: W Proctor; A Richards (S Jones, h-t), N Davies, N Boobyer, G Evans; F Botica, R Moon; R Jones (H Williams-Jones, 49), R McBryde (capt), S Gail, S Ford (V Cooper, 53), M Voyle, H Jenkins (P Morris, h-t), C Wyatt, I Jones.
Cardiff: J Thomas; N Walker, M Hall, L Davies, S Hill; L Jarvis, R Howley; A Lewis, J Humphreys (capt), L Mustoe, K Stewart (L Jones, 66), D Jones, M Bennett (H Taylor, 66), O Williams, J Ringer.
Referee: C Thomas (Skewen).
n Dunvant jumped above both Neath and Ebbw Vale in the Welsh First Division with a 42-17 win over Caerphilly yesterday. It gives the Swansea Valley side a chance of finishing among the top eight who will contest next season's Premier Division.