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.
Christmas has come early at Glynneath rugby club, one of a number around Wales who have received an array of merchandise and equipment this December courtesy of the Welsh Rugby Union's £750,000 participation points scheme.
The WRU have been delivering on the scheme - which gives individual clubs access to up to £5,000 worth of supplies and equipment each for the 2014/2015 season - over the last two weeks and today (Friday) were received by a special guest in Glynneath, club president and pitch marker Max Boyce.
The Welsh Rugby Union has signed a new four year deal with specialist equipment supplier Rhino Rugby, which is set to benefit both the grass roots game in Wales and the national squad in equal measure.
We watch the new grass growing and being stitched together in this week's Principality Welsh Rugby Union Podcast. We speak to Millennium Stadium groundsman Lee Evans, Wales great Ieuan Evans gives an overview on the new strategy announced by head of rugby Josh Lewsey, while we also hear from Bedwas, Aberavon and Carmarthen Quins in the Principality Premiership.
Wales assistant coach Rob Howley was welcomed with open arms by the staff and players at Crymych recently when he hosted a training session in memory of former club captain and coach, Glyndwr Richards.
We hear about the WRU's annual report and some exciting new plans for schools and clubs round Wales in this week's Principality Welsh Rugby Union Podcast. WRU finance director Steve Phillips explains the money side, while head of rugby Josh Lewsey explains his new strategy for schools and clubs. We also get reaction from all round Wales.
The Welsh Rugby Union has launched a nationwide education programme, to help all involved in the game to recognise and remove' players with concussion. Wales, Racing Metro and Lions centre Jamie Roberts Wales assistant coach Rob Howley, WRU Head of Rugby Josh Lewsey and representatives of grassroots clubs in Wales who helped finalise the policy. We also hear from WRU National Medical Manager Prav Mathema, plus Llanelli and Cardiff in the Principality Premiership.
The Welsh Rugby Union has launched a nationwide education programme, to help all involved in the game to recognise and remove' players with concussion. Wales, Racing Metro and Lions centre Jamie Roberts took time out of his club commitments to raise the profile of the campaign launch held at Pontyclun Rugby Club.
The Welsh Rugby Union has launched a nationwide education programme, to help all involved in the game to recognise and remove' players with concussion. Interview with WRU National Medical Manager Prav Mathema.
This week on the Principality Premiership Podcast, WRU TV's Graeme Gillespie talks to Carmarthen Quins head coach Louie Tonkin who is aiming to close the gap on leading duo, Pontypridd and Ebbw Vale, with victory against Bridgend tomorrow.