The Wales outside-half wqas first on the scene after the Leeds Tykes forward was left unconscious in an ugly collision with opposite number Jacques Cronje in the 52nd minute of Wales' 53-18 defeat at Pretoria.
Sweeney rushed to assis the big No.8, checking to see if the unconcious player had swallowed his tounge.
Popham was last night given the all clear to travel home with the rest of the Wales squad after being kept in hospital overnight Saturday with concussion.
But he has Sweeney to thank for rushing to his rescue while he lay motionless on the ground.
"We're all very relieved that Alix is well. He was in a bad way but Ceri reacted first by making sure he didn't swallow his tongue," said Wales captain Colin Charvis.
"Thankfully it was only concussion because it could have been so much worse. It really shook the lads up."
But Sweeney, who replaced Nicky Robinson in the first half of a bruising encounter, played down his role in what was an anxious eight-minute delay to the game.
"I saw Pops lying on the ground and he wasn't moving, so I put my fingers in his mouth to check he wasn't swallowing his tongue," said the 24-year-old. "Thankfully he hadn't and so I just rolled him into the recovery position. I didn't do anything special. I'm just thankful that he's OK."
The incident cast an even darker shadow over a painful day for a second-string Wales side who will want to forget the eighty or so minutes that followed an historic meeting with Nelson Mandela before kick-off.
In the match, Wales found themselves on the wrong side of a seven try scoreline. "We wanted to try a few new things on this tour but our game plan virtually went out of the window with the number of injuries," said Wales coach Mike Ruddock.
"We're highly disappointed with the score but it's been a long season and we will come back from this, especially when we have a few more players back on the field."