In the second half, Williams made a long, winding crossfield run past several defenders, holding the ball in one hand in his trademark style, before sending Nonu over in the corner.
Williams, who replaced Cory Jane on the wing, scored twice, including a try from a centring kick by Richard Kahui, who had another strong game on the wing.
At Waikato Stadium, a sea of black filled every corner, flooding outdoor concessions areas, the concourses and all the stands.
Japanese fans were dotted throughout, waving flags and ostentatiously dressed but overwhelmed by the home crowd.
Before the game started, Junko Kobayashi, originally from Japan but now living in Auckland, was convinced her homeland was about to reverse the 145-17 walloping the team suffered when they last played the All Blacks at the 1995 World Cup in South Africa.
Outside the stadium, punters in the fan zone were upbeat. Six Australians dressed as Japanese sumo wrestlers stood out among the All Black fans who dominated the area.
Despite the large numbers out and about, police said people were well-behaved and there to enjoy the night.
In Auckland, a good-natured crowd crammed into bars around the waterfront - but Captain Cook Wharf did not need to be opened.
Peter Winder, a Government spokesman, was happy with how things turned out, saying the crowd on Queens Wharf peaked at 11,500 during the match. "It was a vibrant atmosphere."
While the numbers fell short of what was needed to open Captain Cook Wharf, he believed that as the tournament progressed, larger crowds would spill over to there.
Meanwhile, measures will be in place tonight to avoid a repeat of the transport disaster that saw 2000 fans miss part of the opening ceremony last Friday.
Those travelling to Eden Park to see Australia play Ireland will benefit from 100 extra buses. There will be greater security on trains and at stations to prevent over-loading and people hitting the emergency stop alarms.
Security guards will also patrol exposed parts of the network where people may access the tracks.