A thrilling first half saw the Scarlets – shorn of their Wales internationals for the trip – denied two tries by the TMO, while the Sharks, whose starting XV was littered with Springboks, were held up over the line.
The Scarlets deservedly crossed for the game’s first try six minutes after the break, with Aaron Shingler touching down.
However, the visitors’ early exertions in humid conditions started to take their toll, and Aphelele Fassi and Curwin Bosch, who also kicked 13 points, both crossed before a penalty try and a Marius Louw score – either side of a Steff Evans consolation – delivered the decisive blow and earned the hosts a bonus point.
A breathless opening almost yielded a try for the Scarlets when Sam Costelow’s determined chase saw him lose out to Fassi by the narrowest of margins.
The visiting fly-half did open the scoring with a penalty after eight minutes, before the visitors had another try chalked off for an Evans foot in touch.
The Scarlets were on top and Costelow added a second penalty to his tally before Bosch halved the deficit from the tee in the 19th minute.
The Sharks’ share of possession and territory increased as the half progressed and Jaden Hendrikse was held up over the line following some desperate Scarlets defending four minutes from the break.
Bosch made it 6-6 at the interval, but the opening try finally arrived for the Scarlets six minutes into the second half when replacement Shingler applied the finish to a well-worked line-out move and Costelow added the extras.
Bosch then missed for a third time in the match but was on target when the Sharks touched down after Hendrikse’s audacious no-look grubber sent Fassi through.
Dan Jones then hit a post as the Scarlets squandered an opportunity to re-take the lead just short of the hour mark, before Bosch showed quick reactions to go over as the Sharks edged clear.
He converted his own score and added another penalty before a tired Scarlets defence was punished with a penalty try.
Louw finished the job after Evans had given Dwayne Peel’s men the narrowest glimmer of hope.