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 Webb Ellis Cup visited Lampeter on Monday to recognise the fact that the town is celebrating a major milestone as it is believed the first ever game of rugby played in Wales, was in fact played in Lampeter 150 years ago.
Cardiff Blues U18 Girls will go into Sunday's Gemau Cymru with an extra spring in their step after Welsh internationals Elinor Snowsill and Philippa Tuttiett offered some last minute tips at a training session earlier this week.
Rob Howley and Josh Lewsey addressed more than 250 community club coaches and referees at the first WRU National Community Conference on the weekend. The volunteers benefitted from coaching masterclasses and workshops in a bid to connect all levels of the rugby pathway in Wales.
UEFA has today confirmed the Football Association of Wales (FAW) has been successful in its bid for the Millennium Stadium to host the 2017 UEFA Champions League Final on Saturday 3rd June, 2017 (kick-off: 19.45hrs GMT).
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.