Newspaper headlines boasted of "history in the making" after the Blue Samurai reached the last 16 for the second time, while television viewing figures nudged past 41 percent despite the game finishing just before 5:30am local time.
The famous "scramble crossing" intersection in Tokyo's Shibuya district erupted in a crescendo of chanting and drumming as more than 1,000 fans clad in Japan's blue team shirts hugged as the final whistle blew.
"I'm still shaking, I just can't believe it," tearful 21-year-old clothes shop assistant Yuka Higashi told Reuters, shouting to be heard over the noise around her. "Honda's amazing!"
Midfielder Keisuke Honda scored Japan's first goal against Denmark in Rustenburg after firing the winner against Cameroon in their opening game.
Screaming fans doused each other with water from plastic bottles at the end of Thursday's match, gleefully ignoring police loudspeaker warnings to "stop being a nuisance!"
Japanese Prime Minister Naoto Kan, on official business in Canada, sent a message of congratulations to Japan, who arrived at the tournament mired in a miserable run of form but now face Paraguay on Tuesday for a place in the quarter-finals.
"I wish to congratulate the team on their excellent achievement," Kan said. "The side has given the whole country energy and pride."
ENERGY DRINKS
Energy drinks were being guzzled by many fans as euphoria gave way to exhaustion and thoughts of a train straight to work.
"I won't get any sleep now," 33-year-old banker Tsuyoshi Hamada said, wincing. "Shower and straight to the office. It's worth it though."
In Osaka, more than 50 fans plunged into the murky waters of the city's Dotonbori river in a repeat of the jubilant scenes of 2002 when Japan reached the last 16 as World Cup co-hosts.
"Don't take the Mickey!" Japan's Brazilian-born defender Tulio told the Nikkan Sports, warning Paraguay they will not get things all their way in the last 16.
"Every last drop!" blared the Sankei Sports, praising the team's endeavour after Japan capitalised on their first World Cup win on foreign soil against Cameroon in their opening game.
Former Japan captain Hidetoshi Nakata, who retired from the game in tears after the country's meek exit from the 2006 finals, added his support.
"That's the sort of game we've wanted to see," he said. "They've grown up at this World Cup. Now let's hope they can go further than we did in 2002."
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