Ryan's injury meant the game ended on a sour note but the match was one the home side won comfortably. Successive defeats to Carmarthen Quins and Pontypridd had hit Llanelli's play-off hopes but scrum-half Gareth Davies bagged a hat-trick as the home side ran in seven tries.
The victory also completed a third successive league double over the Blue & Blacks who last beat Llanelli back in the 2009/10 campaign.
Llanelli flanker Daniel Thomas, who impressed hugely for Wales U20 in their Six Nations campaign, was at the heart of the action as his side came out on top.
It was Cardiff who took the lead though, fly-half Joe Griffin kicking an early penalty before prop Ryan Harford was sin-binned after a quarter of an hour.
Llanelli eventually made the extra man count when Thomas broke and the supporting Davies went over. Full-back Dale Ford atoned for an earlier penalty miss in converting from the touchline but the lead only lasted three minutes.
Ford saw his clearance kick charged down and Cardiff prop Campese Ma'afu did the rest with fly-half Griffin adding the extras.
Scrum-half Sion Hopkins then became the second Cardiff player to be yellow carded in the 35th minute and again Llanelli profited.
From a scrum, Davies crossed for a second try which Ford once more improved on.
Though the 14 men responded via another Griffin penalty, they leaked an important score two minutes into stoppage time.
Llanelli kept the ball alive in contact and fly-half Jonny Lewis was released for a try that Ford converted making it 21-13 at the break.
And the purple patch continued after half time, the home side scoring two tries in as many minutes on the restart.
A Duane Eager break set up a deserved try for fellow flanker Thomas while hooker Kirby Myhill raced through a gap for the home side's fifth try.
It was then the turn of Llanelli to go down to 14 men on the hour. Replacement hooker Craig Hawkins saw yellow and Cardiff replacement prop Jake Cooper-Woolley made the most of the extra space to touch down.
Griffin converted but Cardiff's revival hopes were cut short by a third try from scrum-half Davies with replacement full-back Dion Jones adding the extras.
Ryan's injury held up play for eight minutes and during stoppage time, Llanelli completed the scoring with a try from replacement full-back Dion Jones which he also converted.
The weekend's other Premiership game, the meeting between Bridgend and Llandovery, was postponed due to a waterlogged pitch.