CENTURION, South Africa (Reuters) - World champions South Africa are focused on improving their scrummaging as they seek to wrap up a series victory over Wales in Saturday's second test in Pretoria.

Springbok coach Peter De Villiers demonstrated his displeasure with the scrum by making two of his four changes to the team that overawed the Six Nations champions 43-17 in Bloemfontein last week up front.

"We set a good platform in the first test and I was especially happy with our defence. We want to build on that and the scrums are obviously the one area we are unhappy with," De Villiers told a news conference in Johannesburg this week.

The coach chose debutant prop Tendai Mtawarira and tighthead BJ Botha to partner captain John Smit in a new-look front row as well as recalling Victor Matfield to the second row. Enrico Januarie also returns at scrumhalf.

"I certainly am hoping that the scrums will go better this week," added assistant coach Gary Gold. "We've been a good scrummaging team for a number of years now, and we took a step backwards last week.

"We're quite honest that we let ourselves down by our standards, and we've worked hard under a lot of pressure to perform in the scrums this week. I think it's an area that Wales are going to want to target because they will feel they got the upper hand last week."

Wales coach Warren Gatland also tweaked his front row with Rhys Thomas coming in for Adam Jones at tighthead and Richard Hibbard replacing the injured Matthew Rees at hooker.

"We're looking for more mobility from the tight five, and Rhys may be able to provide that," Gatland said.

"The South Africans carried the ball really strongly and we were a little bit slow getting far side defensively. We've worked on trying to negate them getting across the advantage line as easily and try and limit the number of offloads."

James Hook starts his first international at fullback in a reshuffled backline in which Jamie Roberts moves from 15 to replace Sonny Parker at 12 as Wales search for the first ever win in South Africa.

South Africa - 15-Conrad Jantjes, 14-Tonderai Chavhanga, 13-Adrian Jacobs, 12-Jean de Villiers, 11-Bryan Habana, 10-Butch James, 9-Enrico Januarie, 8-Pierre Spies, 7-Juan Smith, 6-Luke Watson, 5-Victor Matfield, 4-Bakkies Botha, 3-BJ Botha, 2-John Smit, 1-Tendai Mtawarira.

Replacements: 16-Bismarck du Plessis, 17-Gurthro Steenkamp, 18-Andries Bekker, 19-Ryan Kankowski, 20-Bolla Conradie, 21-Francois Steyn, 22-Percy Montgomery.

Wales - 15-James Hook, 14- Mark Jones, 13-Tom Shanklin, 12-Jamie Roberts, 11-Shane Williams, 10-Stephen Jones, 9-Gareth Cooper, 8-Gareth Delve, 7-Jonathan Thomas, 6-Ryan Jones (c), 5-Alun-Wyn Jones, 4-Ian Gough, 3-Rhys Thomas, 2-Richard Hibbard, 1-Gethin Jenkins.

Replacements: 16-T Rhys Thomas, 17-Duncan Jones, 18-Ian Evans, 19-Dafydd Jones, 20-Warren Fury, 21-Andrew Bishop, 22-Tom James.

(Editing by Padraic Halpin)