Williams starred for Wales Under-20s at last year's Junior World Championship and while George North has flown the nest, the Scarlets believe they may have unearthed the next international star.
And on this showing, they may well be right. He scored twice in eight minutes to hand his side an 18-13 lead at the interval and while Edinburgh briefly threatened a comeback, centre Adam Warren scored the decisive try for the Scarlets.
Edinburgh flew out of the blocks and they had the first try of the match after just four minutes when the visitors recycled and put Nick De Luca through out wide.
They had already threatened earlier through Dougie Fife but while the Scarlets had previously managed to defend their line, there was no stopping De Luca - Carl Bezuidenhout nailed the conversion from the touchline.
Edinburgh were 10-0 to the good on 12 minutes when Scarlets captain and No.8 Rob McCusker were penalised at the ruck, Bezuidenhout making no mistake from the tee.
That stirred the Scarlets into life however and with indiscipline creeping into Edinburgh's game, fly-half Aled Thomas notched two quick-fire penalties to reduce the arrears to 10-6.
And the Scarlets had their noses in front on 32 minutes when a fine break from Gareth Davies saw the scrum-half pulled down in front of the Edinburgh line, only for the ball to be recycled to Williams, who dotted down.
Thomas added the extras but Bezuidenhout was on target with a monster penalty soon after to level things up at 13-13.
But just a minute before the break, Williams was at it again, cutting back inside to storm his way over the line. Thomas missed the conversion this time.
Edinburgh began the second half camped in the Scarlets' 22 and, turning down the three-pointer after the hosts were penalised at the breakdown, they eventually had their second try of the match thanks to winger Tom Brown who jinked inside after a fine pass from replacement Harry Leonard.
Leonard missed the conversion, leaving the scores locked at 18-18.
On 57 minutes the Scarlets retook the lead as Warren squeezed through the smallest of gaps after the Welsh side passed the ball along the line, Thomas converting.
Edinburgh hit back just after the hour mark with a penalty from full-back Jack Cuthbert, trimming the gap to just four points.
On 72 minutes Edinburgh were pinged at the scrum and while Thomas missed the conversion, it proved to matter little as the Scarlets held on for the win.
|Scarlets Score Card|
|Edinburgh Rugby Score Card|
|Nick de Luca||1||5|