With both sides already out of the competition, Leicester chose to field a weakened side with no sign of stars George Ford, Jonny May and Manu Tuilagi in their line-up and they were made to pay as the hosts ran in five tries.
Prop Rob Evans scored two of them, Ken Owens, Steff Evans and Johnny McNicholl the others with Dan Jones adding four conversions.
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Will Evans and Mike Fitzgerald scored consolation tries for Leicester.
Scarlets had the better of a scrappy opening ten minutes but play was constantly disrupted by a succession of set scrums and free kicks.
The hosts then had the first opportunity for points but declined a kick at goal in favour of a driving line-out but it came to nothing as they conceded yet another free kick at a scrum.
This forced French referee, Mathieu Raynal, to issue a warning to both front rows as the crowd became restless at the lack of action and it came as no surprise that the first quarter finished scoreless.
Leicester skipper, Matt Toomua’s break was the only highlight of that period but the visitors couldn’t capitalise as a pass from Jonah Holmes went astray with the try-line beckoning.
After 25 minutes, Scarlets opened the scoring with the first try. From a line-out on the visitors 22, Ryan Elias regathered a loose line-out to make a telling burst before David Bulbring and Gareth Davies made darts for the line with Rob Evans on hand to drive over.
Scarlets continued to look the more dangerous side and ten minutes later they increased the lead when a couple of forceful runs from Kieron Fonotia put the opposition defence on the back foot to allow Davies to send Owens over.
Dan Jones converted to give his side a deserved 12-0 half-time lead before Leicester introduced Joe Ford in place of Kyle Eastmond for the restart with Toomua switching to centre.
The change didn’t pay immediate dividends as six minutes into the second half Tigers fell further behind when Evans finished off a driving line-out for his second try before Fonotia carved the defence apart to give McNicholl an easy run-in.
Such was Scarlets’ control that they were able to replace some of their major contributors, Fonotia, Rob Evans and Davies but it made no difference as Steff Evans scored a fifth after Mike Williams was sin-binned for a no arms tackle.
Will Evans and Fitzgerald scored late tries for Tigers but they were comfortably second best.
Jacob Stockdale starred again for Ulster with two tries, with their other score coming from debutant winger Robert Baloucoune, and McFarland admitted it was a special result.
“In the context of who we were playing against and the excitement of the rugby and some of the execution of the plays, it’s certainly up there,” he said.
“When you add into that the atmosphere in the stadium then wow, it was awesome.”
McFarland also applauded the performance of Ireland star Stockdale, saying: “He’s got a bit of stardust hasn’t he?
“There are a lot of tired bodies in our changing room and when you spend a lot of the second half chasing after guys like Leone Nakarawa and his off-loads, and Virimi Vakatawa, that’s hard work.”
Ulster now go to Leicester Tigers for the final round of games sitting in second place on 18 points, three behind pool leaders Racing, who took two points from their first defeat of the campaign.
“We’ve put things back in our control. That’s how we’re looking at it,” said McFarland.