Ruan Pienaar was in imperious form at scrum-half while No.8 Nick Williams was at his destructive best and with Jared Payne's broken-field running lighting the touch paper, Ulster blew the Scarlets away.
But the Scarlets, keen to improve on last weekend's poor showing against Treviso, began the brighter and enjoyed the better of the early possession, taking the lead with a fourth-minute penalty after Dan Tuohy was offside.
Owen Williams, a late addition to the starting line-up after Rhys Priestland failed to come through the warm-up, made no mistake and booted the visitors into a 3-0 lead.
It took less than two minutes for Ulster to hit back however and good work from the Ulster forwards saw Scarlets lock Joe Snyman pinged for holding on - Pienaar kicking the penalty to level things up.
As the half wore on, it was the Scarlets who continued to carry the fight to Ulster but too many errors from both sides crept in and near could create any clear try-scoring opportunities.
But the game was brought to life on 19 minutes with a scything run from Ulster full-back Payne, who signed on for another three years this week, as he romped his way through the Scarlets defence before putting the grubber through and only desperate defence from George North prevented fellow British & Irish Lion Bowe from gathering the ball.
A minute later, both sides were reduced to 14 men when Andrew Trimble and Liam Williams were sent to the sin bin for fighting and it was Ulster who dealt better with the numerical disadvantage.
Pienaar kicked a long-distance penalty to the corner and after his forwards set the position up, the South African fizzed a pass to Bowe on the left who this time beat North to score his 51st try in the competition.
Pienaar added the conversion and Ulster, led by Williams, who was named the RaboDirect PRO12's Players' Player of the Season, turned up the heat.
Pienaar struck the upright with a penalty after Jonathan Davies was offside but when he kicked to the corner on 33 minutes, a textbook Ulster lineout move saw a rolling maul cut through the Scarlets defence before Diack dotted down his seventh score of the RaboDirect PRO12 season.
The conversion from Pienaar struck the post again but he added a penalty on the stroke of half-time after a powerful Ulster scrum to give the hosts an 18-3 lead at the break.
Just three minutes into the second half came the score that appeared to end the match as a contest - Ulster centre Darren Cave making a piercing run following a scrum and while he fell just short of the try-line, prop Court quickly picked up the ball and dotted down.
Pienaar added the extras before a extended passage of stop-start play - thanks in no small part to a serious-looking injury to Scarlets hooker Ken Owens.
On the hour mark replacement scrum-half Davies danced his way through to go over under the posts to give the Scarlets a glimmer of hope but a Pienaar plenty soon after kept them at arms' length.
The Scarlets refused to throw in the towel and did finish the game the stronger, with Timani powering over from close range but they could not get close enough, ensuring Ulster will face either Leinster or Glasgow Warriors in the RaboDirect PRO12 final.
|Ulster Rugby Score Card|
|Scarlets Score Card|