New wing Kristian Phillips rescued the understrength Scarlets with a late try to help see off Italian side Zebre in the Pro12.
This season's newcomers were narrowly ahead at the break and were leading 13-12 before Phillips struck.
Matteo Pratichetti added a try to Daniel Halangahu's two penalties for the visitors.
But Aled Thomas' five penalties and his conversion of Phillips' try gave the Scarlets the edge.
Victory also allowed the hosts to climb into second place in the race for a top-four play-off spot.
In the absence of 12 players on Wales squad duty ahead of the nation's four autumn Tests, the Scarlets had been forced into a glut of changes.
Argentine lock Tomás Vallejos was pressed into back-row duty amid the shortfall while former Ospreys Gareth Owen and Phillips made their Scarlets debuts in the three-quarter line.
Up front Kirby Myhill, 20, stood in for Wales squad hookers Matthew Rees and Ken Owens.
There were also experienced hands among the home squad in Fiji tight-head Deacon Manu and uncapped South African locks George Earle and Johan Snyman.
There was little to recommend about the opening period in which Zebre centre Halangahu out-scored Scarlets fly-half Thomas by two penalties to one.
The only other moment of note in that opening 40 minutes came when Irish referee Dudley Phillips tired of the off-ball niggle that had peppered the encounter.
Centre Owen and visiting flanker Filippo Ferrarini earned 10 minutes in the sin-bin after their clash.
Amid the drab conditions fly-half Thomas levelled eight minutes after the break, then put his side ahead with a third penalty.
However, when the home defence failed to deal with a counter-attack, scrum-half Tito Tebaldi, who had earlier been sin-binned, gathered a loose ball and sent Pratichetti clear.
Pratichetti's midfield partner Halangahu converted only for Thomas to bring his side back to within a point.
Scrum-half replacement Aled Davies' high kick led to Phillips' burst to the line.
Zebre's cover defence failed to deal with what what seemed a benign threat.
But when none of the visitors took responsibility, Phillips plucked the bouncing ball from the air and his pace did the rest.
Thomas converted and as the Zebre discipline cracked under the pressure of their late attempt to regain the lead, the home fly-half added a fifth penalty to seal the win.
VIEWS FROM THE DRESSING ROOM
Scarlets head coach Simon Easterby said: "It was four points, which we desperately needed, but I'd say execution and accuracy, one or two out of 10; effort eight or nine out of 10.
"We put a lot of pressure on ourselves, especially in the first half.
"We played in the wrong areas and second half we did manage the game much better.
"We came away with a win and that's about all we can take away from the game."
Scarlets: Morgan Stoddart, Kristian Phillips, Gareth Maule, Gareth Owen, Andy Fenby, Aled Thomas, Gareth Davies; Phil John, Kirby Myhill, Deacon Manu, George Earle, Johan Snyman, Tomás Vallejos, Johnathan Edwards (capt), Kieran Murphy
Replacements: Aled Davies for G Davies (56), Sione Timani for Snyman (56), Craig Price for Vallejos (71).
Not Used: Hawkins, Hopkins, Peter Edwards, Owen Williams, Nic Reynolds.
Sin Bin: Owen (33).
Zebre: Ruggero Trevisan; David Odiete, Matteo Pratichetti, Daniel Halangahu, Samuele Pace; Paolo Buso, Tito Tebaldi; Matias Aguero, Andrea Manici, Luca Redolfini, Josh Sole, Filippo Cazzola, Filippo Ferrarini, Filippo Cristiano (capt), Andries Van Schwalkwyk.
Replacements: Paolo Buso for Chiesa (69), Carlo Fazzari for Aguero (65), Andrea De Marchi for Manici (79), Luciano Leibson for Redolfini (55), Nicola Belardo for Cristiano (46).
Not Used: Sarto, Caffini.
Sin Bin: Ferrarini (33), Tebaldi (45).
Referee: Dudley Phillips (IRFU)
Assistant referees: Greg Morgan, Alan Jenkins (both WRU)
Citing commissioner: Richard Gwynn (WRU)
TMO: Tony Rowlands (WRU)