Japan shocked world champions New Zealand 14-12 as men's rugby returned to the Olympics after 92 years on Tuesday.
Kameli Soejima got the decisive try midway through the second half, and Katsuyuki Sakai scored on the ensuing conversion to reverse a 12-7 deficit in the sevens match.
New Zealand are 12-time world champions in the sport but this did not help their cause, and their woes also included losing Sonny Bill Williams injured. Williams is the biggest name in the 12-team men's tournament as a two-time World Cup winner with the All Blacks but will plaz no further part in the tournament.
"He suffered a partial Achilles rupture of the left achilles tendon," a New Zealand Olympic team statement said. "He has been replaced by Sione Malia who is one of the New Zealand Olympic rugby sevens team's travelling reserves."
It was Japan's second massive upset in the sport overall after they had last year stunned former champions South Africa at the World Cup.
"It is unbelievable. You never see a minnow come here and beat a team which is supposed to be a gold medal contender. I am still shocked, to be honest," Japan's Lomano Lemeki said.
"We had a game plan against New Zealand - play at our pace and they would get frustrated ... I think we showed that any team can win. If we keep working hard - and I am sure we will."