Nigel Davies saw his men battered into submission, having trailed 13-0 at the interval as ill-discipline reared its ugly head again in Galway.
Vernon Cooper had already been warned by Scottish official Graham Knox but the lock committed a senseless second offence in the 34th minute to leave the vulnerable visitors on the ropes.
By that point, Connacht had already dominated the scrum, line-out and breakdown, and it was no surprise to see the home side capitalise on Cooper’s foul play through number eight Mike McComish’s neatly worked try on the stroke of half-time.
The Scarlets looked down and out but emerged from a lifeless display with a losing bonus point thanks to Lee Williams last-gasp try.
Prior to that, Rhys Priestland had scored a solitary second-half penalty but the Scarlets fly-half lost the kicking battle to opposite number Ian Keatley who fired 11 points as the Irish province ensured Davies’ men join Welsh rivals the Cardiff Blues on their list of home scalps this season.
Admittedly, the visitors were without their Wales squad members Jonathan Davies, Stephen Jones, Martin Roberts, Matthew Rees, Dafydd Jones and skipper Mark Jones for the trip to the Showgrounds.
But coming into the match, the Scarlets had been in a rich vein of form having won their last three fixtures after backing up their stunning success in Europe with a hard-fought Welsh derby win over Newport Gwent Dragons.
The opening exchanges were littered by basic errors and after Rhys Priestland missed a 12th minute penalty attempt, the home side took advantage as ill discipline began to resurface for the Scarlets.
Richie Pugh, Priestland and Cooper were all found guilty of infringements in the space of five minutes and left Davies’ men trailing 6-0 through Keatley’s boot.
In a desperate bid to regain a foothold in the match, Priestland saw an ambitious penalty attempt from inside his own half fall wide but the Scarlets were handed a lifeline in the 26th minute when Connacht centre Keith Matthews was shown a yellow card for a shoulder barge on Evans.
But their own foul play came back to haunt them again when Cooper committed his second offence and joined Matthews in the sin-bin.
The Scarlets forward pack were finding life difficult and even when Tavis Knoyle pinched possession, the scrum-half could only watch on in horror as his 70-metre clearance flew over the try-line.
And it proved costly, as from the resulting scrum, opposite number Frank Murphy made the dart and Johnny O’Connor fed fellow back-rower McComish for a simple score and Keatley’s conversion handed the hosts a comfortable lead.
Connacht prop Brett Wilkinson became the third player binned before Priestland hammered home a 57th minute penalty.
The Scarlets began to build momentum but the home side’s much-improved defence proved too strong a nut to crack before Keatley added his third penalty to seal a hard-fought win with 13 minute remaining.
However, with seconds left on the clock, Davies’ men claimed a losing bonus point when wing Williams scorched over in the left corner for a converted try.
