BRIGHTON, England (Reuters) - Samoa expect South Africa to come out with all guns blazing in their rugby World Cup encounter on Saturday as the Springboks look to atone for their 34-32 defeat to Japan.

The loss, described as the greatest upset in the history of the tournament, would ensure South Africa are fully focused for the game at Villa Park, said Samoa coach Stephen Betham.

"We know there will be probably be a backlash but we're going to be ready for it," he said as the Pacific Islanders began preparations for the clash.

Samoa, looking to reach the quarter-finals for a third time, got their campaign started on Sunday with a 25-16 victory over the United States.

"The tier one nations all got a wake-up call after Japan beat South Africa," added Betham. "Our surprise factor is gone and they are going to come with all guns blazing."

However, he was not convinced that Japan's shock win demonstrated a closing of the gap between the established powers and the rest.

"That's a hard one. We look for consistency, we haven't struck that yet. We play well, then we play below average but that consistency is something we are still fishing for," he said, adding that Japan's win had not altered Samoa's planning.

"We must understand this is a World Cup and every country has brought its best team and everyone starts off on a level field.

"And whoever takes their chances on the day will be very hard to beat."