The Scarlets finished with a 25-20 win over the Irish province at Athlone’s Dubarry Park.
It was the Welsh side that registered the first score after 16 minutes, from the boot of outside-half Gareth Bowen.
Two minutes later the tournament’s top points scorer later converted centre Matt Watkins’ try, as Llanelli’s prop David Maddocks collected a 22 drop out, and the forwards formed a powerful maul, eventually working the ball to the backs for a 13-0 lead.
Bowen added a penalty on 20 minutes before Llanelli began to dominate. Watkins had sidled through the Connacht line from 15 metres out, but scrum-half Mike Phillips out-did him after 33 minutes when he muscled past four Connacht tacklers from a scrum 35 metres out, to ground Llanelli’s second try under the posts.
The conversion was added, before Connacht’s woe continued as they opted to kick for touch in first half injury time, lost lineout possession and ended the half scoreless and 20 points in arrears.
Connacht saw full-back Mark McHugh skew two lengthy penalties wide in the opening half, before Eric Elwood reduced the deficit on 50 minutes with a penalty on the Llanelli 22 for their first points.
The 24-year-old Tal Selley angled his run perfectly from his centre position six minutes later to touch down for the visitors, away to the right touchline, for an evidently crucial score.
Bowen missed his fifth kick of the night before flanker Ian Boobyer was sin-binned for deliberately going to ground on the hour mark.
Elwood thumped over the resulting penalty before Llanelli’s composure wavered with number eight Scott Quinnell receiving a yellow card for a suspected punch.
Llanelli conceded two Connacht tries in the final quarter with wing Connor McPhillips crossing for his fourth league score and centre Darren Yapp ghosting through poor Welsh tackling on 74 minutes. Outside-half Elwood converted both before Quinnell’s return steadied the visitors’ ship and sent them towards the Celtic League’s summit.