"We have lost the series but we still have a lot to play in the final game. Hopefully we will win tomorrow and from there onward it could be a different story," Harbhajan told reporters on the eve of the match.
"The ODIs are coming up and then the Tests. We want to play our best game tomorrow and we want to put up our best show. Once we start winning we will be a difficult side to beat."
Citing example of the recently-concluded Test series in Sri Lanka where India bounced back to win the series after losing the first match, Harbhajan said: "It was because of the belief that we had.
"Every game is a challenge for us from here on. Yes we have lost the series and we didn't play as well as we should have but Eden is always a very special ground for all of us.
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"Obviously winning here will mean a lot to us. We will go out there and give it our best shot. If we win here, we will take that confidence into the ODI series," he said.
"I don't think we need to worry too much about the losses in our last two games. We are hurt by those losses but going forward and talking about the World Twenty20," he said.
Harbhajan, who's India's highest wicket-taking offspinner, said it's about backing their spinners ahead of the next year's World Twenty20.
"I think it is important to back the players who are probably the best players for the format. This has been the quality of this team; they have stuck to the players who they believe can win the game.
Looking ahead to the World Twenty20, Harbhajan said spinners would play a crucial role if they're to regain the title that they had won in 2007.