Scrum-half Williams and prop Thyer make up two of a handful of changes to the team that lost to Leinster by a solitary point last weekend, with Wales winger Tom James returning.

Aled Summerhill starts at outside centre and Dan Fish at full-back, with Rhys Patchell moving to fly-half, while hooker Matthew Rees is recalled.

And as the Blues seek to avoid a third GUINNESS PRO12 defeat in a row, Wilson knows they will be presented with a tough test by Ulster.

"Tomos Williams and Brad Thyer have both impressed in recent games and deserve starting positions," said the head coach. "We're looking forward to seeing how they both perform from the start of the game.

"It's another crucial home game at a venue where we are always extremely motivated to win.

"We are back in front of our passionate home supporters and we were very disappointed to lose last weekend. We need to bounce back with a win.

"Ulster are a good side, home or away they always perform, and they have depth to their squad, despite international call-ups.

"They are a very dangerous side and they will be motivated by the narrow loss to Scarlets last weekend. Ulster play good open rugby so it should make for an entertaining game."

The Blues' only victory over an Irish province in their last seven such encounters was 20-16 at home to Connacht in December, while they have won only one of their last seven clashes with Ulster.

Ulster, meanwhile, saw a three-game winning run in the GUINNESS PRO12 came to a halt by the narrowest of margins at home to Scarlets last weekend.

But he Ulstermen have not lost successive regular season games in the same season since December 2014 and they won 19-12 against Newport Gwent Dragons on their most recent visit to Wales.

Paddy Jackson will captain the visitors at fly-half, with Ruan Pienaar joining him in the half-backs and Sammy Arnold and Luke Marshall partnered in midfield together for the first time.

John Andrew, who made his first Ulster start on Sunday, is joined in the front row by props Callum Black and Bronson Ross, while Nick Williams returns from injury to start at No.8, with Robbie Diack and Chris Henry on the flanks.

Ricky Lutton and Sean Reidy, who both signed contract extensions earlier this week, are on the bench and Pienaar is eager to ensure Ulster bounce back from last week's defeat at the first time of asking.

"We still have loads to play for," he told the Irish News. "That's the beauty of rugby, you always get another chance.

"Seven days is a long time. The guys have done a lot of soul-searching and a lot of analysis. We need to have a good look at ourselves, hopefully that will show on the pitch on Sunday."

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At BT Sport Cardiff Arms Park, 2.30pm. Live on S4C/BBC Sport NI
Referee: John Lacey (IRFU, 49th competition game)
Assistant Referees: Dan Jones, Gwyn Morris (both WRU)
Citing Commissioner: John Charles (WRU)
TMO: Jon Mason (WRU)