Scarlets hooker Rees replaces Bath's Lee Mears while Ospreys prop Jones comes in for Phil Vickery who had a torrid time in the scrum. The clash will see an all-Welsh Lions front row for the first time since 1955.
But while there was good news from a Welsh perspective with the promotion of Rees and Jones, there wasn't such good news for Ospreys second row Alun Wyn Jones who has been dropped to the bench with the bulkier Simon Shaw getting the nod.
The other changes concern the backs where Ireland's Rob Kearney takes over from injured Lee Byrne at full-back and Luke Fitzgerald replaces Ugo Monye on the left wing.
British and Irish Lions team to play South Africa
at Loftus Versfeld, Pretoria on Saturday, 2pm:
R Kearney (Leinster and Ireland); T Bowe (Ospreys and Ireland), B O'Driscoll (Leinster and Ireland), J Roberts (Cardiff Blues and Wales), L Fitzgerald (Leinster and Ireland); S Jones (Scarlets and Wales), M Phillips (Ospreys and Wales); G Jenkins (Cardiff Blues and Wales), M Rees (Scarlets and Wales), A Jones (Ospreys and Wales), S Shaw (Wasps and England), P O'Connell (Munster and Ireland, capt), T Croft (Leicester and England), D Wallace (Munster and Ireland), J Heaslip (Leinster and Ireland).
Replacements: R Ford (Edinburgh and Scotland), A Sheridan (Sale Sharks and England), A-W Jones (Ospreys and Wales), M Williams (Cardiff Blues and Wales), H Ellis (Leicester and England), R O'Gara (Munster and Ireland), S Williams (Ospreys and Wales).