The 38-16 loss at Apia Park, Samoa's fourth successive test defeat, reduced them to 16th in the world rankings, their lowest position since the index was introduced in 2003.
Head coach Alama Ieremia said everyone was hurting and he accepted that all results, good or bad, ultimately came back to him.
"I'm the head coach so I take full responsibility for anything that happens in the campaign so I've got no issues with that," he said.
"We've got to look at myself and see whether we actually dropped the ball and go through a review process to see where we could have done things better and if we missed anything.
"We've got to review the players as well and we've got to have a good look at our preparation and all of that. So I've got no issue with taking full responsibility, it is my job and I've got to find out the answers as soon as possible."
Ieremia said Fiji took their chances at key moments in the game and earned their status as top team in the region.
"Still a lot of disappointment sort of lingering around and ... we didn't create enough pressure to really test the Fijians early in the second half and that was costly in the end," he said.
"We played a very good Fijian side who took their opportunities, especially early in that second half. Those two early tries - once they created those it was always going to be tough to pull back and with the wind behind their backs they did very well to come up with the win."
The Manu now face a home and away play-off next year against a European qualifier and Ieremia urged disgruntled fans to keep the faith.
"They're very passionate people and that goes to show that they actually really care for the team, which is great and I understand the frustration is there but a two-point loss to Wales and that four-point loss against Tonga - the team is not far off it," he said.
"Those two test matches could have gone either way and when I look at the positives of this team I'm confident that it's heading in the right direction and I'm confident I can do the job for this team."
Portugal, Spain or Russia loom as likely contenders for Samoa in next June's play-off, according to Ieremia.
"Then obviously the winner (of the playoff) goes straight through into Pool A (at the World Cup), which will be with Ireland, Scotland and Japan," he said.
"It's pretty straight forward but that's obviously a long way away so we will get through the next few weeks first and review and look at how things could have been done better here."
Fail in that playoff and Samoa will still have a chance to reach the World Cup via next year's repechage playoffs that will feature the winner of August's Oceania Cup clash between the Cook Islands and Tahiti.
Photo: PHOTOSPORT Samoa were thrashed 78-0 by the All Blacks in June, before defeats against Wales, Tonga and Fiji.