Rabbitohs forward Angus Crichton.

South Sydney coach Anthony Seibold labelled his side's execution as "unacceptable" after they were beaten 24-12 by Canberra at GIO Stadium on Saturday afternoon.

Following nine straight wins earlier this season, the Rabbitohs were firming as Telstra Premiership favourites a few rounds ago.

The wheels have fallen off dramatically, with today their third successive defeat.

Up 12-0 early, the away side appeared to be well placed to revive their fortunes.

Four unanswered tries for the Raiders, many scored off the back of pressure created from cheap turnovers, allowed Ricky Stuart's men to earn just their second win over a top eight side this year.

"The Raiders were outstanding last week, so we were prepared for their best," Seibold said.

"I thought our effort areas were much improved from last week, I'm really disappointed with our performance today, but our effort areas were really high.

"From our point of view, it is just unacceptable to make continual errors, and then expect to win games at NRL level."

With just a 62 per cent completion rate, 17 errors and 10 penalties, the visitors were second best in a number of areas.

"We didn't build any pressure, eight errors on tackle one and tackle two, we didn't create fatigue," Seibold added.

"The Raiders had 59 play the balls inside our 20 metre zone....they are crucial attacking indicators in the competition.

"In the end, they came home stronger than us."

Even the return of injured trio Greg Inglis, Alex Johnston and Campbell Graham didn't provide major additional spark.

"It was good to be back personally,'' Inglis said when quizzed on how his thumb held up across the 80 minutes. "I'm more concerned about our team and what we can do to improve next week.

"We just need to be very diligent in what we do, we have trust in our process...we just have to execute it now."