Scarlets returned to the top of Guinness PRO14 Conference B but had to withstand a second-half comeback before beating the Blues 30-17 at Parc y Scarlets.
The home side saw an 18-3 interval lead reduced to a single point before they secured a try bonus point 10 minutes from time.
Scarlets' tries came from centre Hadleigh Parkes, hooker Ryan Elias, replacement scrum-half Jonathan Evans and wing Steffan Evans, with Leigh Halfpenny supplying two penalties and Rhys Patchell a conversion.
Wing Willie Halaholo and replacement scrum-half Lloyd Williams crossed for the Blues.
Scott Williams was named Scarlets captain for the game five days after being omitted from the Wales squad, and he partnered New Zealand-born Parkes, who could play for Wales in the autumn after qualifying on residency.
Rey Lee-Lo returned to Blues' midfield among five changes from the team that won at Toulouse in Europe last weekend.
Scarlets went into half-time with a more than useful 15-point lead following a rather forgetful 40 minutes for the Blues, who suffered three injuries and a sin bin for No. 8 Nick Williams.
Halfpenny and Jarrod Evans swapped penalties before the home side stamped their authority on the contest with a try for Parkes after seven minutes.
The Blues failed to secure possession from a restart and Scarlets went on a concerted attack which saw Parkes sprint in from 20 metres.
Winger Blaine Scully, tight-head prop Dillon Lewis and Evans were all replaced as injuries added to the Blues' problems.
And their chances of getting back into the match were dealt a blow when Nick Williams was sin-binned after foul play at a ruck, although Scarlets failed to add to their lead during the 10 minutes he was off the field.
A Scott Williams try was disallowed for a knock-on but a minute later Elias was over after an impressive drive from a line-out.
Blues looked as if they may cut the deficit before the break but Halaholo lost the ball over the line.
In the space of seven minutes the Blues were back within a point -- Halaholo was put into space by Steven Shingler and ran unopposed to the line from just outside the 22, and then Johnny McNicholl was caught in defence allowing Lloyd Williams to squeeze over.
However, just as Blues were turning the screw the momentum changed dramatically from the restart as replacement Jonathan Evans latched on to Steffan Evans' angled kick through.
With 10 minutes left Steffan Evans crossed for the bonus-point try after a period of pressure on the Blues' line.