The Cameroon defence failed to cut out Daisuke Matsui's cross to the back post in the 39th minute and Honda reacted quickly. The CSKA Moscow midfielder produced a superb first touch before clipping the ball beyond stranded goalkeeper Hamidou Souleymanou.
Japan then defended resolutely to regain that winning mentality after a run of five warm-up matches without a victory. Honda's career is on an upward curve as he joined CSKA at the turn of the year from Dutch club VVV Venlo and helped the Russian club reach the quarter-finals of the Champions League.
He said: "This goal was a nice birthday present for me. I am so happy now and there is a great atmosphere in the team. We were able to stop Cameroon's attacking players and I think that was why we were able to get a good result. We had confidence before the game. Of course we played badly in the friendly matches but we didn't mind about this because they were not so important. We were only concentrating on today."
The closest Cameroon came to finding the target arrived five minutes from time when Stephane Mbia's effort hit the bar. With the talismanic Samuel Eto'o tightly marked it was a frustrating afternoon for one of Africa's brightest hopes. Coach Paul Le Guen's aim going into the tournament was to try and emulate the team of 1990 that reached the quarter-finals.
However, with Group E rivals Holland winning earlier in the day in the group, his side face an uphill struggle. Le Guen said: "Of course I am upset that we have lost the game but our attitude was wrong.
"We were tense and nervous, especially in the first half. We did not show what we are capable of. We were not at our level and kept losing possession. It now means we have to win our next game against Denmark. I hope we recover well and go on and do our best."
In contrast Japan coach Takeshi Okada could afford a wry smile after the game. He said: "We knew Cameroon would be physically strong and so it proved. But my players had a strong motivation to do well. They asked me before the match if they could stand with shoulders linked at the national anthem. I thought it was a good idea."