Watkins proved to be a constant thorn in the Edinburgh defence
Scarlets: (21) 42
Tries: S. Jones, Watkins (2), King, MacLeod, Thomas
Cons: Jones (5), Thomas
Edinburgh: (10) 17
Llanelli Scarlets scored three tries in each half as Edinburgh put up little resistance at Stradey Park.
Tries: Jacobsen, Callam
Stephen Jones, Matthew Watkins and Regan King crossed in the first half, Allan Jacobsen's try keeping the visitors in touch at 21-10 down.
Scott MacLeod and Dave Callam exchanged tries soon after the break but two quick-fire tries took Scarlets clear.
Watkins grabbed a second, Jones adding a fifth conversion, before Iestyn Thomas wrapped things up on 64 minutes.
Impressive young full-back Morgan Stoddard created the first score for Jones with 12 minutes on the clock when he burst past the gain line and popped the ball up for his supporting fly-half.
Edinburgh's Phil Godman cut the deficit with a penalty, but two midfield howlers by Edinburgh then allowed the Scarlets to score twice in two minutes.
Watkins intercepted Godman's long pass inside his own half to score under the posts, and then the ball was presented on a plate for King to follow suit.
Jacobsen only had five yards to cover to score his try to give Edinburgh a glimmer of hope on 25 minutes, but McLeod's one-two with Gavin Evans - on for the injured Mark Jones - put the Scarlets in control again.
A Scarlets turnover allowed Callam to score Edinburgh's second try, but the result was put beyond doubt with 15 minutes remaining.
Centre Watkins, the Magners League's second highest all-time try-scorer, showed typical fleet of foot to dance through the Edinburgh defence to score his second.
And then replacement prop Iestyn Thomas galloped over, Ceiron Thomas converting after coming on for Jones.
Scarlets: Stoddart; Daniel, King, Watkins, M. Jones; S. Jones, L. Davies; Manu, Owen, J. Davies, Cooper, MacLeod, D. Jones, Bater, Popham.
Replacements: G. Evans for M. Jones (21), C. Thomas for S. Jones (60), Stuart-Smith for L. Davies (74), I. Thomas for Manu (57), Rees for Owen (57), Afeaki for MacLeod (71), N. Thomas for Popham (71).
Edinburgh: Cairns; Dewey, Di Rollo, Dey, Webster; Godman, Laidlaw; Jacobsen, Kelly, G. Cross, Strokosch, Pringle, Taylor, Hogg, Callam.
Replacements: Lopez Fleming for Di Rollo (65), Senio for Laidlaw (51), Lawrie for Kelly (67), Hewett for G. Cross (73), Rennie for Hogg (63).
Not Used: Bentley, Hodge.
Ref: Peter Fitzgibbon (Ireland).