Thomas returns to the starting line-up after making an appearance from the replacements bench last week kicking the winning penalty in the final moments of the game. Fellow outside half Steve Shingler suffered a medial ligament knee injury in the victory over the Scots and is expected to be out of action for up to 10 weeks.
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.
The victory over Edinburgh kept Scarlets in the top four and only a point off leaders Ulster, reflecting on the win Pivac said: "It was a critical game for us. We have to make sure we do well in home games. It was a very, very important game for us.
"The boys have shown all year long that they're fighting for every point and every win. It's one of those seasons where we've had a few tight ones. It's nice to come out on the right side of a few of them. It's an improvement on last season but we still have a long way to go."
Looking ahead to Sunday's game he said: "At the moment they're sitting at the top. 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."
Scarlets team to take on Ulster on Sunday 21st February, kick-off 2.30pm, at Kingspan Stadium;
15 Michael Collins, 14 Gareth Owen, 13 Regan King, 12 Hadleigh Parkes ©, 11 DTH van der Merwe, 10 Aled Thomas, 9 Aled Davies, 1 Phil John, 2 Kirby Myhill, 3 Peter Edwards, 4 George Earle, 5 David Bulbring, 6 Aaron Shingler, 7 Will Boyde, 8 Morgan Allen
Replacements: Ryan Elias, Dylan Evans, Rhodri Jones, Maselino Paulino, Rory Pitman, Rhodri Williams, Dan Jones, Steffan Evans
Guinness PRO12 Scarlets News
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