The West Africans must overcome South Korea on Tuesday night in Durban and need Argentina to beat Greece in the other Group B match in Polokwane to stage a stunning turnaround in their fortunes.
"The attitude in the group has been very good so I'm very positive about the game," he told a news conference.
"Then we need Argentina to beat Greece, but I think we've got a good chance of getting a result against South Korea."
Lagerback, who led his native Sweden to the second round of the last World Cup, said but for "small margins" his team could have had two victories in their campaign so far.
He said he would respect Maradona's decision if the Argentine coach rested players against the Greeks but still thought the South Americans would prevail.
"What I have learned from 30 years as a coach is that nothing is impossible but I expect Argentina will beat Greece," he said.
Midfielder Dickson Etuhu, who played in both of the defeats to Greece and Argentina, said contrary to media reports in Nigeria, the mood in the camp had been "unbelievable."
"We're all together, we've always been together," said the English-raised central midfielder.
"I don't really know where you get that information from but we're all together and we're looking forward to the game tomorrow and we want to get the win.
"This is our Cup final, we have to go out and show big heart, desire. It might not be pretty at times, but we have to go out and get the result," he added.
South Korea coach Huh Jung-moo has said his team would be out to wind up the Nigerians, hoping they would emulate their team mate Sani Kaita, who was dismissed for kicking out at a Greek defender last week.
"I doubt any other Nigerian player will get a red card," said Etuhu. "We have learnt that lesson."
Lagerback said defenders Taye Taiwo and Elderson Echiejile, who were both injured in the Greece match, had trained on Tuesday and things "looked positive" for them to be fit to face South Korea.
There was a "chance" that Nigeria captain Nwankwo Kanu would make his first appearance of the finals at the Moses Mabhida stadium although he would not be unveiling his line-up until he had spoken to the players.
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