Scarlets opened their Guinness Pro14 campaign with a hard fought victory in the torrential rain at Parc Y Scarlets.
First-half tries from Steff Evans and Paul Asquith built a useful platform for the home side, with Dan Jones adding eight points with the boot.
Connacht's points in the 18-10 defeat came from an Eoghan Masterson try and a penalty and a conversion from Connor Fitzgerald.
Wales props Rob Evans and Samson Lee and wing Steff Evans were included in Brad Mooar's first competitive line-up. All three were omitted from Wales' World Cup squad.
Centre Steffan Hughes led the Llanelli-based team in the absence of Wales hooker Ken Owens. Prop Paddy McAllister made his league debut after joining Connacht from Gloucester and Fitzgerald was at fly-half, with Jack Carty on Ireland duty in Japan.
The visitors made a lively start but a well-drilled Scarlets defence were able to snuff out an attack which went through 20 phases.
When the Scarlets got the ball in attack they always looked dangerous and the stalemate was broken on 20 minutes when wing Evans squeezed over in the left corner.
The quality of the match at times left a lot to be desired, not helped by persistent rain.
But five minutes from half-time Scarlets grabbed a second try. Hughes dummied to kick superbly before putting Asquith over under the posts. Jones added the conversion.
Connacht had the last say of the half, however, when Fitzgerald kicked a 39th minute penalty.
Jones restored his side's 12-point lead four minutes into the second half with a penalty after Connacht centre
Tom Daley was yellow-carded for a professional foul on his own line. However,Connacht responded positively when some persistent pressure on Scarlets' line was rewarded with a try for Masterson, converted by Fitzgerald.
In deteriorating conditions Scarlets eased the pressure with a Jones penalty from a high tackle giving them an eight-point advantage on the hour.
That was the extent of the scoring, although eight minutes from time Jones missed a penalty from right in front of the posts after Connacht had been penalised at a scrum.