Roberts is looking a strong contender for a Test spot at centre
Jamie Roberts is looking forward to joining fellow Lions debutant Keith Earls against a Royal XV on Saturday as he launches his bid for a Test place.
"[Ireland's] Earls is such a talented player, he's absolutely lightning - I didn't realise how quick he was until training this week," said the Welshman.
"It's a chance to stake a Test claim, we'll all be chomping at the bit."
Roberts, 22, is one of seven Welshmen in the team for the tour opener in Rustenburg, three more on the bench.
Lee Byrne, Shane Williams, Matthew Rees, Adam Jones, Martyn Williams and Andy Powell also start along with the Ospreys' Ireland three-quarter Tommy Bowe, while Alun Wyn Jones, Mike Phillips and Stephen Jones are replacements.
"It'll help to have so many Welshmen around, we know so much about each other's games," said Blues centre Roberts.
"It will be tough in the altitude and heat, but we've been training hard and are looking forward to it.
"We've done quite a lot of analysis on their key individuals, but there's only so much you can do - it's about how we play as a team."
Roberts, who won the first of his 12 caps in last year's Six Nations and has since faced South Africa three times, was seen as a strong pre-tour contender for the inside-centre berth.
His imposing 6ft 3in, 16st 11lb frame has caused the Springboks problems in the past, and he could form a formidable midfield partnership with Brian O'Driscoll.
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