Rhys Priestland put the boot into his former team at a rainswept Parc-y-Scarlets as Bath claimed an impressive 18-13 European Champions Cup away win.
The ex-Scarlets number 10 kicked six penalties from seven attempts in wet and windy conditions to give Bath a second successive Pool Five victory.
Despite Steff Evans, who is favourite to take over from an injured George North in Wales' autumn Tests, scoring a brilliant first-half try, the Scarlets suffered a second European defeat five days after being beaten narrowly by Toulon.
Fullback Leigh Halfpenny added two penalties and a conversion, but the Scarlets are now up against it in terms of potential quarter-final qualification, while Bath can build towards December home and away appointments with Toulon in confident mood.
The weather wrecked hopes of a free-flowing spectacle, and Wales international Priestland took the opportunities that came his way, amassing all of Bath's points.
Captain Ken Owens returned to the Scarlets' line-up after being on replacement duty last weekend, while Hadleigh Parkes featured alongside Jonathan Davies in midfield and Gareth Davies was at scrum-half.
Bath were without flanker Francois Louw due to a three-week suspension, with Priestland being joined in the team by fellow Wales internationals Taulupe Faletau, Luke Charteris and Aled Brew.
The heavens opened well before kick-off, but it did not unsettle Bath as they immediately found impressive pace and rhythm with Faletau leading the charge into Scarlets' 22.
The pressure resulted in a sixth-minute penalty that Priestland, who scored more than 1,000 points during his Scarlets career, effortlessly landed the kick, only for Halfpenny to boot an equalising strike just three minutes later.
A second Priestland penalty quickly restored Bath's advantage, only for the Scarlets to conjure a magical try that evoked memories of their title-winning campaign in last season's Guinness PRO12.
Fly-half Rhys Patchell freed Evans 10 metres inside his own half after initial handling that defied the elements, and after Davies took on the move at pace before he was tackled by Anthony Watson, Evans swooped to gather possession and finish brilliantly.
Halfpenny added the conversion as Bath were left reeling by a score that said everything about the Scarlets' renowned attacking ambition and intuitive support play.
Watching Wales head coach Warren Gatland, who names his squad for the autumn Tests early next week, could not fail to have been impressed by Evans' finishing prowess, but Bath quickly cut the deficit to a point when Priestland completed his penalty hat-trick.
And when Scarlets prop Samson Lee was penalised for a high tackle, Priestland again made no mistake, preserving his 100 per cent record off the tee to give Bath a 12-10 interval lead.
Scarlets looked to have put themselves in serious trouble eight minutes after the break when Patchell's attempted clearance kick was charged down by Priestland, who hacked ahead and attempted to regather, but the television match official ruled he had knocked on as he slid over the line.
It was a major let-off for the home side, but they fell further behind to another Priestland penalty as French referee Romain Poite continued to punish Scarlets' technical indiscipline.
And a sixth Priestland penalty 12 minutes from time sealed the deal for Bath, before a Halfpenny strike at least secured his team a losing bonus point.
