Eric Elwood kicked a penalty deep in injury time to deny the Celtic League title-chasing Scarlets victory in a seven-try thriller at Stradey Park.
Scarlets (20) 33
Tries: Griffiths, Watkins, Selley.
Cons: G Bowen 3.
Pens: G Bowen 4.
Connacht (13) 33
Tries: Munn 2, Mostyn, Penalty.
Cons: Elwood 2.
Pens: Elwood 3.
The Scarlets scored regularly as Bryn Griffiths, Matthew Watkins and Tal Selley crossed for tries, while Gareth Bowen made all seven of his kicks.
The the Irish earned a bonus point by scoring four tries through Wayne Munn (2), Matt Mostyn and a penalty try.
Bowen's late kick looked to have won it for Scarlets before Elwood struck.
Connacht gave away two kickable penalties within the first five minutes - one from former Newport wing Mostyn - and Bowen put the Scarlets into an early 6-0 lead.
But Elwood steadied any Irish nerves with a penalty kick the first time Connacht got into Scarlets territory.
That seemed to be the spark the visitors needed, as they drove to within 10 metres of the Welsh try line.
Scrum-half Mike Walls took a quick tap penalty, catching the Scarlets snoozing, and fed wing Munn for a try, Elwood's conversion making it 10-6 to Connacht after 10 minutes.
The Scarlets hit back to retake the lead within five minutes, the catalyst a pick-and-drive through a ruck from wing Salesi Finau.
Scott Quinnell charged into the Connacht midfield and the number eight's magnificent off-load allowed lock Griffiths in under the post for a converted try.
Elwood kicked the scores level 13-13 just before the half-hour mark but within seconds of the restart Quinnell was bursting through again, timing another perfect pass for skipper Watkins to score under the posts.
Bowen's conversion meant the Scarlets led 20-13 at half-time, stretching that advantage with another converted try within a minute of the restart.
Finau surged down the left touchline, dragging two Irish tacklers with him, and the Tongan's inside ball allowed Selley to race 35 metres for the Scarlets' third try of the night.
Connacht replied by working their skipper Darren Yapp through a hole in midfield, albeit with a hint of blocking, and Mostyn went over for an unconverted try in the left corner that closed the gap to 27-18.
Both sides lost men to the sin-bin, Connacht back row John O'Sullivan for punching and Scarlets fly-half Bowen for stamping.
But the Irish played the numbers game better and Yapp sent Munn through for his second try, timing a fine inside pass to his wing coming back against the grain.
Bowen arrived back on the field just in time to strike his third penalty kick and give the Scarlets a seven-point cushion.
Connacht nearly levelled things when substitute Conor O'Loughlin was held up over the line, but detroyed the Welsh pack from the resulting five-metre scrum to earn a penalty try.
Elwood's conversion made it 30-30 with four minutes remaining, ensuring an exciting match would have an equally thrilling ending.
With a minute of normal time remaining Bowen maintained his 100% kicking success with a penalty to edge the Scarlets ahead.
But fittingly Elwood ensured it would end with honours even, slotting his third penalty deep in injury time.
Scarlets: Davies, Evans, Selley, Watkins (capt), Finau, Bowen, Phillips, Maddocks, Gravelle, Thiel, Griffiths, A Jones, Hodges, Boobyer, S Quinnell.
Replacements: J Davies, I Thomas, Cooper, Wyatt, E Lewis, Burn, Rees.
Connacht: Mostyn, McPhillips, Yapp (capt), McHugh, Munn, Elwood, Walls, McFarland, Jackman, Clarke, Browne, Farley, Neville, Lacey, O'Sullivan.
Replacements: Fogarty, Bracken, Swift, Carter, O'Loughlin, Moore, Meagher.
Referee: Mike Hall (SRU).