Samoa's stunning Test victory over Australia shows the national side is capable of winning this year's Rugby World Cup, Prime Minister Tuilaepa Sailele Malielegaoi says.

Tuilaepa said on Monday he is "over the moon" after the 32-23 victory over the Wallabies in Sydney, a win he said "warmed the heart" of the Pacific Island nation.

"No-one actually thought that Australia would lose," he told reporters.

"I myself knew we would be competitive, as the way we played in the Northern Hemisphere tour showed we can compete.

"But defeating Australia, which is the second-ranked team and is twice world champions, shows Samoa can win the World Cup."

Former Samoan captain Pat Lam, who coaches the Blues Super Rugby team, said the win ranks alongside the team's shock 16-13 victory over Wales at the 1991 World Cup as the country's best sporting result.

"It's massive, right up there," he told Radio New Zealand.

"Australia's number two in the world currently ... (we) had no chance, according to the Aussie media and that's probably the worst thing you can say to a Samoan.

"They had a real belief and determination and their preparation has been very good.

"The real key is they didn't just beat them, they out-fought them, out-muscled them and out-played them completely. It was a great win."

Lam rejects the argument that Australia lost because they had not fielded a full strength team, saying Samoa also had key players missing.

"At the end of the day, they put out what they believed was their best Test team and Samoa put out what they had available and they absolutely hammered them," he said.

He said Samoa face a difficult task at the World Cup in New Zealand, starting in September, as they are in the so-called "pool of death" with South Africa, Wales, Fiji and Namibia.

But he is confident the Samoans can reach the quarter-finals.

"South Africa, they'll be tough, Wales always has an issue with Samoa at World Cup time and there's Fiji," he said.

"So it's certainly a winnable pool, but it'll be a tough pool."

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