Jordan Williams kicks a penalty against Llandovery.
Llanelli will play Pontypridd in next Saturday's Premiership final following their derby win over Llandovery at Church Bank.
Anthony Buchanan's side were deserved 29-20 winners but Llandovery remained in it until the final moments.
In the end Llanelli's four tries were enough, Kristian Phillips giving them an early lead with an interception try. Nic Reynolds added a second and scores from Daniel Thomas and Jordan Williams after the break secured the win.
Williams kicked two conversions and a penalty but Llandovery refused to go away, Shaun Miles and Kieran Murphy their scorers.
James Garland converted both tries and kicked two penalties but Llanelli deservedly went through.
It had been a nightmare start for Llandovery, scrum half Rhodri Williams throwing a speculative pass which was intercepted with ease by Phillips. The right winger galloped his way to the line and with Williams adding the conversion, Llanelli led 7-0 with less than a minute on the clock.
An early score gave Llanelli confidence and they were dominant in the early exchanges, full back Dion Jones going close to scoring before being tackled into touch. But despite seeing most of the ball, Llanelli failed to extend their advantage and when Garland replied for the Drovers with a pair of penalties, they were only ahead by one.
In a tight encounter, both sides were guilty of some poor tactical kicking but it was Llandovery who were making more mistakes as they struggled to retain possession. And the visitors took advantage with a second try before the interval.
Reynolds had earlier made a superb break which saw him carve through the Llandovery defence and he was at his attacking best again, powering through to touch down by the posts. Jordan Williams converted but that was not the end of the first half scoring.
Llandovery had been nowhere near their best throughout the first 40 but after Miles crashed over and Garland nailed the difficult touchline conversion, they only trailed by a point at the break.
The half time score was perhaps not representative of Llanelli's dominance as Llandovery failed to click. But when Williams kicked his first penalty of the day at the start of the second half, Llanelli were up and running. Another try soon arrived, Thomas continuing his impressive scoring record following some stylish Llanelli back play. Williams missed the conversion but his side looked well on top.
Despite boasting a comfortable advantage, Llanelli seemed determined to keep their opposition in the game and as they did in the first half, they let Llandovery back into it.
Scarlets' No. 8 Murphy, who is leaving the region at the end of the season, dived over for Llandovery's second try with Garland again converting.
And as the rain lashed down at Church Bank, it was now the home side who were on top. They battered the Llanelli line with wave after wave of pressure but a third score failed to arrive as the red defence held firm.
Indeed Williams could have pushed Llanelli further clear but saw two penalty kicks and a left footed drop goal effort go wide.
It failed to matter though and the Llanelli fly-half made amends for his kicking to seal the win with a late converted try of his own.
The winners of a filmmaking competition organised by the education charity Into Film and the WRU enjoyed a behind the scenes tour of the Millennium Stadium - and a chance to be photographed with the WRU's fire-breathing, rugby loving mascot, Scorch The Dragon, and Welsh international, Jake Ball.
Ebbw Vale coach Jason Strange is proud of his side's effort in against Pontypridd in the Principality Premiership final and as WRU TV's Liz Jones finds out, he's now looking forward to Wales' Under 20 campaign with confidence.
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WRU National Academy Coaching manager Allan Lewis will retire, a new Elite Coach Development Manager post has been created and WRU international skills coach Jason Strange will now fulfil his WRU role on a full time basis.
Wales U20 bounce back in the World Rugby Championships in this week's Principality Welsh Rugby Union Podcast. We hear from forwards coach Geraint Lewis and captain Ollie Griffiths, plus new WRU head of physical performance Paul Stridgeon. We talk new facilities in Usk and hear the plans of new Cardiff Blues head coach Danny Wilson.
The Crawshay's WRU President's XV returned from a gruelling two-match tour of Georgia undefeated after a try by Llandovery's Shaun Miles in the last move of the game ensured a 14-9 victory over Emerging Georgia at Rustavi Stadium on Saturday.
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SSE SWALEC Cup
The SSE SWALEC Cup, Plate and Bowl continue the legacy of the WRU Challenge Cup, culminating in a shot at glory at the Millennium Stadium
Women's Community Rugby embraces both the regional and community club game from Girls' Leagues through to the Women's Premier Division