"It all came down to a question of concentration," Keshi told reporters. "We switched off for the second goal and it cost us the game.
"Nevertheless, I'm very proud of what my boys did, considering the difference in experience between the two sides. I hope we can maintain this standard and just up the concentration levels a bit and be a little more professional."
The African champions must defeat Spain on Sunday and hope that Tahiti beat Uruguay in order to qualify for the knockout stages, but Keshi said that his team will be fired up despite elimination being all but certain.
"We can't wait to play them," he added. "Anything can happen. That's what makes this such a great game."
Nigeria beat Tahiti 6-1 in their first game.