The former kings of the one-day game have not beaten a Test side in a one-day international since June 2009 and went down to a seven-wicket defeat against Graeme Smith's men in their World Cup opener in New Delhi on Thursday.
But a surprisingly upbeat Sammy, whose side is now ranked below Bangladesh, refused to give up hope after the match, backing his players to hit back.
"I think we've got to have that self-belief. We know what we are capable of doing and as long as we play to our full potential we could beat any team on the day. But we just have to be consistent in our performances."
The skipper said it was crucial his team made the most of situations when they were on top after the West Indies squandered good positions. They looked strong at 113 for one at one stage and were also well placed at 178-4.
"Before the match everybody was uncertain as to how the pitch would play but looking at it we should have scored 270-plus on the wicket," Sammy said.
"I think losing the wickets in clusters really hampered our total. We had guys getting starts but they didn't carry on," the 27-year-old added.
Sammy also rued missed chances to dismiss Smith and century-maker AB de Villiers in the South African innings.
"We created opportunities but we didn't capitalise on them and AB de Villiers batted like a senior player and that brought South Africa home."
"We saw how de Villiers applied himself and batted through and scored 100 so I think you just have to apply yourself like in any cricket, whether it be Tests, Twenty20, you've got to be out there in the middle to really score runs," he added.
Sammy said he was happy with the balance of his side, which contained all-rounders Dwayne Bravo, himself and Kieron Pollard, despite the lack of specialist bowlers.
"I think the guys who were picked in the eleven to bowl were quite capable of doing the job. Like batting, we too have to be consistent in our line and length and create pressure.
"Obviously we have another game. We'll come up and see what areas we could improve and come up with the best possible attack to play on."
One bright spot for the West Indies was the sparkling World Cup debut of Darren Bravo, the half-brother of Dwayne, who hit 73 runs.
"Most people compare him to Brian (Lara) and he really looks like Brian. He's a good asset for us," Sammy said.
"That was the kind of innings we knew he could play and all I would say is that he needs to go on when he gets to 50, to transform it into a 100 which I'm sure he will do before this World Cup is over," the captain added.
West Indies face the Netherlands in their next match in New Delhi on Monday.
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