LONDON (REUTERS) - South African coach Heyneke Meyer apologised to his country for what he said was an "unacceptable" performance by the Springboks as they lost to Japan on Saturday in the biggest upset in Rugby World Cup history.

Speaking to reporters after the Pool B match at Brighton Community Stadium, Meyer said: "I have to apologise to the nation. It was just not good enough. It was unacceptable and I take full responsibility."

Meyer was left to rue his team's ill-discipline in an encounter strewn with penalties.

"Every time we got playing we scored tries, but our discipline was just not good enough. You can't give away soft penalties. There are no easy games in this competition."

South Africa's Fourie du Preez, who plays his club rugby in Japan, described the result as the low point of his career and said the Springboks had been "outsmarted".

"I've been playing there (Japan) for four years, so I knew what was coming. I tried to let the guys know during the week that they are a proper nation.

"They were probably just better prepared than us, they had a lot of focus areas where they targeted us. They just outsmarted us."

Springbok captain Jean de Villiers told BBC reporters that South Africa could still bounce back.

"There is still a possibility to make it out of the group and we need to win every game we have left, but it is hugely disappointing. The character of this side will be tested. It is not doom and gloom but a massive dent to us."