Ulster leapfrogged over the Welshmen after a tense battle to take over the Celtic League leadership.
Ulster (10) 10
Scarlets (9) 9
Pens: Bowen 2
All the points came in the first half with Ulster's Bryn Cunningham scoring the only try and fly-half Adam Larkin landing a conversion and a penalty.
The Scarlets, who made mass changes to their starting line-up, did not give up their top spot easily.
They replied with a drop goal from scrum-half Mike Phillips and two penalties from Gareth Bowen.
There was little between the sides, although the visitors to a noisy Ravenhill looked to have the power up front until they fizzled out after the break.
Ulster missed their international half-back pairing of David Humphreys and Neil Doak with their general play very static.
It was only the industry of their pack that finally allowed them to succeed.
Ulster were quickly into their stride when they surged ahead in the fourth minute.
Wing Scott Young, a late replacement for Ireland call-up Tyrone Howe, pierced the Scarlets defence, fed Roger Wilson who made ground before feeding Cunningham who dived in at the posts.
But after their fast start, Ulster appeared to switch off and allow Scarlets to dictate play with strong pick and drives upfield.
Scarlets got on the scoreboard in the 13th minute when after Bowen saw a short-range penalty rebound off the posts, scrum-half Phillips popped over a drop goal.
Chris Wyatt battled hard for the Scarlets
The Scarlets pack continued to rumble upfield to keep Ulster on the back foot.
Bowen found his range in the 18th minute to further narrow the leeway after Ulster were caught offside.
Ulster were punished again for an indiscretion in the 37th minute with Bowen landing his second penalty to give his side the lead for the first time.
But the lead was short-lived with Larkin banging over a long-range penalty in the third minute of first half injury time.
With the rain sweeping in behind their backs, the Scarlets began to turn the screw with Chris Wyatt making a good job of disrupting Ulster┐s line-out.
Scott Quinnell was lucky not to receive a yellow card when he was blatantly offside in stopping Ulster receiving good ruck ball.
From a promising position Larkin was wide off the mark with the resulting penalty.
There were few thrills and spills as the half went on and even fewer try-scoring chances particularly with both sides void of any international squad players.
Any chances that came were available came Ulsters way as their pack matched the Scarlets' ferocity up front.
Ulster: B Cunningham, J Topping, S Stewart, P Steinmetz, S Young, A Larkin, K Campbell, R Kempson, P Shields, R Moore, M McCullough, R Frost, A Ward (capt), N Best, R Wilson.
Replacements: M Sexton for Shields (46), S Best for Moore (46), M Mustchin for Frost (46), W Brosnihan, N Doak, P Wallace for Stewart (34), T Bowe.
Scarlets: B Davies; T Selley, M Watkins, L Davies (capt), S Finau; G Bowen, M Phillips; P John, A Gravelle, J Davies, V Cooper, C Wyatt, D Hodges, G Williams, S Quinnell.
Replacements: D Maddocks, A Yelland, A Jones for Wyatt (57), G Quinnell, D Burn, G Evans, R Rees for Davies (22).
Referee: Andy Ireland (Scotland)