Pivac has made two changes to the side that secured victory over Edinburgh last Friday night, forging a new half-back pairing of Aled Thomas and Aled Davies.
Maselino Paulino is named on the replacements bench as he makes a return from his suspension with young outside half Dan Jones released from Wales Under-20s for the weekend's action.
And Pivac believes his side can take confidence from the way Newport Gwent Dragons ran Ulster close earlier this month, losing 17-15 in Belfast.
"At the moment they're sitting at the top," he said. "We'll take some confidence from Dragons' performance out there and the fact that they were very unlucky to get the result.
"On the day, if you can string a good performance together you're in with a good shout. Hopefully we'll do that on Sunday afternoon.
"It's important to get a good start; we don't want to be chasing the game, they're a really good crowd and get behind the side.
"We will be looking to chip away at the scoreboard and stay in the game. Hopefully we'll get some reasonable weather and try to score some tries."
Ahead of Saturday's games, Ulster top the GUINNESS PRO12 table on points difference from Connacht and are also the best team in the tournament on current form having gained 22 league points from their last six matches.
The Ulstermen have not lost at home to a team from outside the island since Glasgow visited the Kingspan Stadium in September 2013.
Meanwhile, Scarlets' last four GUINNESS PRO12 fixtures have all gone with home field advantage whilst the Welshmen have not won on the road in the competition since they visited Benetton Treviso in early December.
Scarlets won 22-12 when the two sides met in Llanelli in September and have not achieved a season's double over the Ulstermen since 2008/09.
Roger Wilson will line up for Ulster for the 200th time, while Rob Herring has a slight hamstring injury so John Andrew will make his first senior start, at hooker. Herring's absence also means that out-half Paddy Jackson will skipper the side for the first time.
Wilson will be joined in the back row by Robbie Diack and Chris Henry, who will start for the first time since December after fully recovering from injury.
Paul Marshall will partner Jackson at half-back, with Luke Marshall returning from international duty to take a place at inside centre alongside Darren Cave.
The back three remains unchanged from the win over Glasgow last week, while Kiss can call on experienced half-back duo Ruan Pienaar and Ian Humphreys from the bench.
And Paul Marshall is confident that, despite international absentees, Ulster have the resources to preserve their place at the top.
"The guys that have come in over the past few weeks have done very well," said the scrum-half.
"They are putting pressure on the so called regular players to make sure they can get their places back and that is healthy for a squad.
"But whoever is at the top of the table everybody wants to knock them off. That has been our goal when we're not up there. We're now going to be targeted by everybody."
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At Kingspan Stadium, 2.30pm.
Referee: Ian Davies (WRU, 41st competition game)
Assistant Referees: Nigel Correll, John Carvill (both IRFU)
Citing Commissioner: Eddie Walsh (IRFU)
TMO: Alan Rogan (IRFU)
Live on BBC NI and S4C
1st Floor Simmonscourt House
Ballsbridge, Dublin 4, Ireland