There have not been many surprises at this World Cup but this probably counted as the biggest shock so far. Japan came to South Africa in such a state of chaos that shortly before setting out for Bloemfontein, their midfielder, Keisuke Honda, asked Japanese journalists if they really thought they would lose all their group games. He was met by an embarrassed silence.
After a series of warm-up matches that had seen them surrender four of their five friendlies, Japan could claim to be, in terms of form, the worst side at this World Cup. The celebrations when the final whistle went in a Free State Stadium that was far from full were spontaneous and genuine.
Japan manager Takeshi Okada's prediction that he would lead his side as far as the semi-finals in South Africa might still seem ridiculous, but at least a man who regards himself a master strategist has surpassed his three successive defeats in the 1998 World Cup.
By doing so he has confounded his critics and left Africa re-assessing their favourites for glory. With Ivory Coast, Cameroon could probably claim to be the pick of the continent's teams but yesterday they became the first to lose.
It was not that Japan dominated, it was that they took the one chance that fell to them.
A Cameroon attack led by Samuel Eto'o and supported by the talents of Pierre Webo and Eric Choupo-Moting, a young German-born forward who had made a dramatic impact in the Bundesliga with Nuremburg, did not.
Six minutes before half-time, Honda managed to escape his marker, Stephane Mbia, controlled Daisuke Matsui's cross and slotted the ball past Hamidou Souleymanou. Aside from a drive from Shinji Okazaki that struck the outside of the post but was ruled offside, it was the only time Japan threatened.
Paul le Guen, who has been given a Sven Goran Eriksson-sized salary to transform Cameroon, would have been bitterly disappointed with his side's response. Eto'o, a man who had won successive Trebles with Barcelona and Internazionale, had been irritated by criticism from Roger Milla, the man who had driven Cameroon to the quarter-finals in 1990, that he seldom reproduced his club form for his country. If this was his opportunity to shut Milla up, he failed to take it.
Marshalled by Tulio Tanaka, the Japan defence succeeded in forcing Eto'o, deployed on the right, deeper and deeper; while Le Guen's decision to bring on Geremi, who had lost the captaincy to Eto'o as a sop to the striker, appeared an admission of sorts.
Cameroon rallied but it was late and met by bad luck. Five minutes from time, a blistering drive from Achille Emana slammed against Eiji Kawashima's crossbar and in the final minute of stoppage time, the Japan keeper reacted brilliantly as Webo met a low cross. The Japanese bench erupted. This was their first World Cup victory outside their own country and there were some who might have been happy to return home with just a point.
Japan (4-5-1): Kawashima; Komano, Nakazawa, Tanaka, Nagatomo; Matsui (Okazaki, 69), Honda, Abe, Hasebe (Inamoto, 88th), Endo; Okubo (Yano, 82).
Cameroon (4-3-3): Hamidou; Mbia, Nkoulou, Bassong, Assou-Ekotto; Matip (Achille Emana, 63), Makoun (Geremi, 75), Enoh; Eto'o, Webo, Choupo-Moting (Idrissou, 75).
Referee: O Benquerenga (Portugal).
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Yuko Yasui, 33, is an art student in London but hails originally from Nagoya.
I was so relieved when the final whistle went! We did not play as well as I expected but thankfully Cameroon played even worse than us. As soon as Keisuke Honda scored I wanted the game to be over as after that, our attack did not look like scoring and our defence looked unsettled at times. Honda was our best player and we were lucky to win. Thankfully, Yuji Nakazawa was solid enough at the back, defending well and keeping the Cameroon attacks at bay, ensuring we held on to our lead. I was surprised how poor the African side were with only [Samuel] Eto'o and [Benoit] Assou-Ekotto standing out. If they had been stronger, I am sure we would not have won.
We will need to improve if we are going to beat the Netherlands on Saturday and although we won I don't think we will qualify if we carry on playing like we did. Going into the game, our coach, Takeshi Okada, could not decide who was going to start and after that performance I am sure he will still be wondering who to start with against the Dutch.