Behind by six points in the closing stages, Connacht refused to settle for a losing bonus point and, roared on by the home crowd, pushed for the converted try they needed, but their hopes were dashed when Jonathan Davies intercepted in the final minute and streaked clear.
After a scrappy start by both sides at a windswept Sportsground, it was Connacht who drew first blood - out-half Miah Nikora slotting home his first penalty of the afternoon on ten minutes, seven minutes after Rhys Priestland missed his first effort for the Scarlets.
That boosted the home side who embarked on a fine running move that swept from left to right and Connacht captain Gavin Duffy looked well-placed to grab the first try of the match, but wing Tiernan O'Halloran did him no favours with a wayward pass.
The Scarlets, league leaders going into round two of this season's RaboDirect PRO12, responded in feisty fashion and Nick Reynolds was making headway down the left after a burst from North which caused panic in the Connacht defence but the winger could not force his way through.
On the half hour mark, Scarlets flanker Josh Turnbull made a powerful burst through the middle but Connacht's Andrew Browne made a try-saving tackle to maintain the hosts' slender lead.
And as half-time approached, Connacht found themselves with possession in the opponent's half and they made it pay despite needing two attempts to score the try.
Some fine hands from Connacht's big forwards appeared to have put Eoin Griffin in on the left-hand side but the Scarlets held the centre just short but from the resulting scrum the ball was spread back over to the right, allowing Griffin to dot down in the corner.
Nikora's conversion attempt dropped short however, leaving Connacht to take an 8-0 lead into the half-time interval.
After the break the Scarlets came out firing and it was unsurprising that North was at the fore.
The Wales international powerhouse made all the running before finding 18-year-old full-back Williams who crossed the whitewash for his first RaboDirect PRO12 try before Priestland converted to trim Connacht's lead to just one.
On 47 minutes, Priestland missed a good chance to give Scarlets the lead but he also struggled with the wind and he pushed his effort wide despite having plenty of distance.
But the wave of Scarlets pressure was to tell just two minutes later - North steamrollering his way down the right wing to grab his fourth try of the season. Priestland was wayward with the conversion again however.
Connacht were shell-shocked and the Scarlets threatened to streak clear when the slippery Williams jinked his way over for his second try of the match on 52 minutes but the wind was playing havoc for Priestland.
He failed to add the extras and after weathering the storm, Kiwi Nikora finally scored Connacht's first points of the half on 62 minutes to take them to within a score of Scarlets, 17-11 down.
It looked a case of how many Scarlets would rack up but some stoic Connacht defence, and a few knock-ons when the visitors were well placed, meant they failed to add to their total.
And in the closing stages, the hosts threatened to steal an unlikely victory - a forward pass denying flying winger Fetu'u Vainikolo the chance to open his legs - but Scarlets had the final say as Davies eased over and Willams converted.
|Connacht Rugby Score Card|
|Scarlets Score Card|