The gloom, he said, was compounded by this week's bombing in Nigeria which caused the death of at least 13 people among fans gathered to watch a match taking place at the finals in Brazil.
Nigeria, playing at their fifth World Cup, disappointed in the Group F match against Iran on Monday after Argentina had beaten Bosnia 2-1 in Rio de Janeiro on Sunday.
"It's not a pleasant thing to see people die for no reason. It was probably a double jeopardy after a game when most Nigerians were not happy we had a tie against Iran," Keshi told reporters.
"It was very tough for us. Our heart goes out to them. We will do everything possible to make sure we put a smile on Nigerian faces tomorrow," he said ahead of Saturday's match at the Pantanal arena (2200 GMT).
Keshi was confident his team would improve on their opening performance and get a good result for their demanding fans.
"Nigeria is a different place. They want to win at all costs. They appreciate football. Whatever happened against Iran they felt that was not our best and they felt disappointed. They felt we didn't perform highly," he said.
Keshi, an African Nations Cup winner as player and coach, denied his team had played nonchalantly against the defensive Iranians.
"We didn't have a nonchalant attitude there. For the first 20 to 25 minutes we tried to make a difference, but anxiety (set in and) we couldn't keep up our style of play," he said.
"Tomorrow it will be a different game, Bosnia has a different style, a different mentality and I think we're ready," he said.

"We have to check mate the Bosnians,” he added.
Keshi said Nigeria would do all they could to maintain the good name of African football at the finals after defeats for Ghana, Cameroon and Algeria and three points out of six for Ivory Coast.
"It is not so great for our African continent. But I think we have one or two teams still on that can probably do something for the continent," Keshi said.
"But if you look around it is not just Africa. You look the champion of the world, out after two games. There are no more little teams in the world. We will try as hard as we can to make the continent proud,” he added. 


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