Celtic League champions Scarlets had to endure a spirited late comeback from The Borders to secure victory.
Borders (0) 15
Tries: Moffat, Cusiter
Scarlets (21) 26
Tries: Finau, Wyatt, G. Thomas, Easterby
Cons: Bowen (3)
Tries from Salesi Finau, Chris Wyatt and Gavin Thomas, all converted by Gareth Bowen, gave the visitors a 21-0 lead at the break.
Charlie Hore and Gareth Morton missed penalties for Borders but Stuart Moffat managed a 51st minute touchdown.
Simon Easterby powered through for the fourth Scarlets score but Borders' Chris Cusiter managed a late try.
The first hour of the match followed the form-book, as the champions dominated.
But the Borders refused to buckle completely and looked the stronger outfit in the frantic closing stages.
In the opening minutes, Borders had earned a chance to break the deadlock when the Scarlets wandered offside in their own danger zone.
Kiwi stand-off Hore, making his competitive debut for the pro-team, connected crisply - but the ball drifted off course and crashed back from the post.
Scarlets made the most of their reprieve by surging up field to seize the initiative.
Bowen sent a pinpoint chip into space, giving left-wing Finau plenty of time and space to scoop it up and score in the corner.
Then Test lock Wyatt was driven over by his powerful pack colleagues - then flanker Thomas was in the right place at the right time to finish off a sweeping handling move.
Hore was offered another penalty opportunity to claw back three points, but his luck was out again as the 40-metre effort flew wide of the target.
It was the same story when Gareth Morton took over the kicking duties before the interval.
Borders came out at the restart with more purpose, but there was another dose of frustration as winger Nikki Walker failed to latch on to an interception with the line at his mercy.
They eventually got off the mark when ex-Glasgow star Stuart Moffat pounced on a loose ball to dash 35 metres for the try.
Hore then found his touch with the boot to slot a penalty - but any prospect of a shock comeback was snuffed out as Simon Easterby powered through to score.
Borders had the last word when scrum-half Cusiter sneaked in for their second touchdown, goaled by Hore.
"It's early days in the season, so I'm very pleased to get the win and bonus point," said Scarlets coach Gareth Jenkins.
"I was very pleased with our set piece, that helped us put some good things together, especially in the first half.
"The second half was disappointing, but credit to the Borders, they're a lot better team than last year with better balance and structure."
Borders coach Steve Bates had mixed feelings after the game, saying: "I'm pleased with our overall performance but frankly disappointed we didn't win.
"We stood off them early on. In the second half we changed our tactics and came at them."
Borders: G Morton; S Moffat, C MacRae, A Davidson, N Walker; C Hore, C Cusiter; P Thomson (capt), S Scott, B Douglas, S MacLeod, C Stewart, S Gray, W McEntee, M Blair.
Replacements: R Ford, M Parr, G Cross, A Rennick, B McKerchar, A Warnock, J Steel.
Scarlets: G Evans; A Havili, T Selley, M Watkins, S Finau; G Bowen, M Phillips; I Thomas, M Rees, J Thiel, B Griffiths, C Wyatt, S Easterby (capt), G Thomas, S Quinnell.
Replacements: J Davies, C Hawkins, V Cooper, D Jones, A Powell, D Peel, A Thomas.
Referee: Simon McDowell (Ireland)