It was a game, Powell believes Wales should have won if it was not momentary lapses in concentration.
"It was good to be back," said Powell. "I've been struggling with a bit of a groin injury but it's great to be back in the shirt and I'm just gutted that we lost.
"We always come so close. We went two scores up and should really have put the game to bed. It's just little things that in the end turn into big things that cost us the game.
"Everyone played well one to 22, but it's just key moments of games - losing the ball or kicking too long. The boys are gutted.
"The first half we were in control, playing in the right areas of the pitch and we wanted to go out and do the same in the second.
"It's not psychological. It's in our back yard, we should be favourites and it's only a matter of time until we beat one of the big boys.
"We just switched off for 10 -15 minutes and it cost us. We were kicking the ball away and giving them too much ball. They hung on and took one or two opportunities more than us.
"South Africa are always physical but we had them on the ropes. They were blowing. Our fitness is definitely better but they slowed the game down which was frustrating.
"If we want to be the best we have to bounce back. It's going to be a big game against Fiji on Friday and the boys will have to be in great form."
South Africa now travel to Murrayfield to face Scotland before taking on England. They will hope to maintain their 100 per cent record in Europe so far this season as they go in search of a rare Grand Slam.