The Scarlets produced an excellent second-half display to sweep aside Leeds with ease in the Powergen Cup.
The Welsh side had led their English rivals by just 6-0 at half-time after two kicks by Gareth Bowen.
But after the break, Leeds' defence capitulated and the Scarlets ran in three tries courtesy of Tal Selley, Iestyn Thomas and Matthew Watkins.
Leeds found their way over the line in the dying minutes courtesy of Rob Rawlinson but it was too late.
Both sides looked intent to attack from the outset but struggled to find a way through, so much so that the only points in the opening 40 minutes were a drop goal and a penalty from Bowen.
After the break, though, the shape of the game changed as Selley opened the Scarlets' try-scoring account in the 53rd minute following some fine link-ups between Bowen and Watkins.
"We had a lesson in the contact area; Simon Easterby was world class and that's where the game was lost"
And despite Bowen's subsequent missed conversion, the visitors stretched their advantage to 14-0 when Bowen fared better with a penalty attempt.
The game was effectively ended as a contest with two Scarlets tries in the space of just four minutes.
After some sustained forward pressure, Thomas did enough to bulldoze his way over the line in the 65th minute.
And moments later Watkins intercepted Leeds full-back Iain Balshaw's pass to score under the post.
Balshaw tried to make amends by playing a part in Rawlinson's consolation try before Leeds walked off the park still without a win this season.
"I'm very disappointed. We had a lesson in the contact area; (Simon) Easterby was world class and that's where the game was lost.
"The Scarlets are a top side and I find it amazing at times the way people write them off in Wales.
"But some of our young players did well and they'll learn a lot from that."
"We set our stall out with the intention to go and play and this week it paid off for us.
"First half we spilled a lot of chances and it looked as though Leeds were still in the game at half-time.
"We stepped it up in the second half and scored some nice tries, but Newcastle next week will be tough."
Leeds Tykes: Balshaw; Rees, Jones, Vickerman, Biggs; Ross, Marshall; Kerr, Bulloch, Gerber, Hooper, Morgan, Dunbar, Parks, Crane.
Replacements: Isaacson, Rawlinson, Murphy, Thomas, McMillan, Stimpson, De Marigny.
Scarlets: Byrne; James, Watkins, King, Selley; Bowen, Peel; Thomas, Gravelle, J Davies, Afeaki, John, Easterby (capt), Mills, Popham.
Replacements: R Davies, Hawkins, Wyatt, Quinnell, L Davies, Hercus, Daniels.
Referee: Tony Spreadbury (Bristol)