Scotland captain Greig Laidlaw feels Springbok wing JP Pietersen should have received a yellow card for a dangerous tackle on Tim Swinson in the Boks' 34-16 Pool B win in Newcastle on Saturday.
Referee Nigel Owens penalised Pietersen, after consulting the Television match Official George Ayoub, but did not issue a yellow card for the offence.
"Looking at it at the time, I felt: how can that not be yellow?" said Laidlaw.
"That probably never cost us the game – it was our inaccuracies more than anything."
Laidlaw did spend 10 minutes in the sin bin himself, after he tackled Bryan Habana without the ball during the second half.
"It was a physical game and I think we probably lost that battle, especially in the first half," he added.
"We were on the back foot and that sucks the life out of us.
"We just needed more good play and we could have caused them problems; that was maybe the most disappointing thing.
"We never played well in the first half, we got back in touching distance and I think we dropped the next kick-off and let them off the hook."