The previous best men's shot put result was Les Mills' seventh at Tokyo in 1964.
Walsh earned the right to his gong among a dozen men grunting as if shifting pianos up spiral staircases. He said good riddance to the 7.26kg iron sphere with customary venom and never wilted as the pressure ramped up to mimic that of a hyperbaric chamber.
Walsh was fourth, but level with Franck Elemba from the Republic of Congo until his fifth of six heaves. Elemba was ahead by virtue of his better second throw of 21.00m, a personal best.
Then the Kiwi uncoiled.
"It wasn't my best work, but you've got to take it don't you," he said in the aftermath.
"There was a lot of pressure around but it was a hell of a competition with the Americans throwing that well. I guess I smashed it bro'.
"It's great to know I'm first [among New Zealand male field athletes]. I just thought I was in better nick, it wasn't quite flowing like normal."
Walsh beat two-time defending Olympic champion Tomasz Majewski, former world champion David Storl of Germany and Commonwealth Games champion O'Dayne Richards on his way to the prize.
Walsh has built a considerable pedigree since taking bronze at the 2014 world indoor championships in Poland. He finished fourth at last year's world championships and won the world indoors this year with a personal best of 21.78m, defeating his competitors by 89cm.
He beat every major international competitor across the 2015 season and became the first New Zealand man to win a Diamond League meet, in Brussels.
During his rise to throwing stardom, he has refused to relinquish his tool belt at Mike Greer Homes in Christchurch.
Walsh is a throwback to a generation of Kiwi athletes who contested major competitions while seeking leave from work. That suits him fine.
He often refers to getting a good-natured ribbing from his workmates asking why he didn't throw further. He will no doubt be answering the same questions and shouting drinks upon his return.
Walsh and fellow Kiwi Jacko Gill were the first New Zealanders in 40 years to feature along side each other in the final of an Olympic track and field event. In 1976 Dick Quax earned silver and Rod Dixon finished fourth in the 5000m.
Gill finished ninth with a best of 20.50m. He was forced out of the top eight by Majewski's final throw of 20.72m.
Walsh and Gill qualified with the second and fourth best throws respectively.
Walsh needed one attempt -21.03m - to reach the automatic qualifying standard of 20.65m. He chilled out as much as possible to take his mind off the sport's show piece and to avoid feeling "flat as a pancake".
Gill threw within 3cm of his personal best. He heaved 20.80m with his third and final attempt, despite battling a broken right foot.
Crouser threw the best qualifying attempt with 21.59m.
