Tries from Sammy Arnold, Leva Fifita, and John Porch on his 50th appearance for the province, as well as fourteen points from the boot of Jack Carty wrapped up a deserved win for the Westerners on a momentous night for Kieran Marmion, who made his 200th appearance for the club.
The home team scored two tries of their own, but the visitor's defence -- despite being down to fourteen men on two occasions -- held firm, mirroring their set-piece, which was efficient on both sides of the ball.
It was the hosts who began on the front foot and they made their ascendancy count when Dan Jones opened the scoring with a penalty.
Three points soon became seven when Johnny Williams collected a sweetly struck grubber kick to touch down under the posts. Jones made no mistake from the tee and The Scarlets lead 10-0 with the first half approaching its halfway mark.
With Cian Prendergast and Fifita prominent with their carrying and in defence, however, Connacht worked their way back into the game.
From a quickly taken free-kick, the Scarlets attempted a cross-field kick, but Tom Daly was alert to it and brilliantly fielded the ball. Then, showing deft hands, the Carlow man fed his centre partner, Arnold, to run in the score from just outside the 22.
With the wind in their sails, the away team tagged on another score through a Carty penalty to narrow the deficit to two points at 10-8 approaching the half-hour mark.
The Westerners made it three unanswered scores in a row and took the lead for the first time in the game when Carty calmly kicked a penalty that was earned by great work by Niall Murray and Dave Heffernan after a line out, which was a pattern that would emerge throughout the game.
Scarlets broke the sequence of Connacht score when Jones added another penalty to help the hosts retake the lead at 13-11.
Not panicking, though, the away team made sure they went into the break leading. A scrum in the Scarlets 22 gave Connacht the platform to attack. Paul Boyle’s big carry made the initial burst. Prendergast then added his carrying duties before Fifita completed the move by powering over the line.
Carty nailed the conversion and Connacht lead 18-13 at halftime.
The Westerners began the second half in a similar manner with attacking intent. They were rewarded for it when Carty coolly kicked a three-pointer to grow the away team's lead to 21-13.
Connacht were dominant as the second half progressed – impressing on both their throw and the Scarlets’ at line out time – and it yielded another score when Carty tagged on a penalty to take the score to 24-13.
The set-piece once again provided a platform for a Westerners score when – after their surging maul was stopped – Connacht elected to release the backs. Double centurion Marmion fed Daly and the centre bagged his second assist of the night by passing to Porch to touch down to take the score to 29-13 to the visitors.
The flow of scores for the Westerners was broken when the Scarlets were awarded a penalty try. Fifita was shown a yellow card in the process and the away teams lead was cut to nine points at 29-20.
The hosts put on the pressure for a route back into the game and they were helped when Connacht were once again reduced to fourteen when Fifita was unfortunate to receive a second yellow card. Pathcell slotted the resultant penalty and the lead was cut to six.
However, with the line speed in defence strong the Westerners held out and claimed their first ever win away to the Scarlets
15: Tiernan O’Halloran
14: Peter Sullivan
13: Sammy Arnold (replaced by Tom Farrell)
12: Tom Daly
11: John Porch
10: Jack Carty
9: Kieran Marmion (replaced by Caolin Blade)
8: Paul Boyle (replaced by Abraham Papali’i)
7: Jarrad Butler
6: Cian Prendergast
5: Leva Fifita
4: Niall Murray
3: Tietie Tuimauga (replaced by Jack Aungier)
2: Dave Heffernan (replaced by Shane Delahunt)
1: Jordan Duggan
16: Shane Delahunt
17: Greg McGrath
18: Jack Aungier
19: Eoghan Masterson
20: Abraham Papali’i
21: Caolin Blade
22: Conor Fitzgerald
23: Tom Farrell