While the 15-a-side World Cup winner made a big impact in his sevens debut on Saturday, he finished the tournament in awe of his less-heralded teammates after New Zealand pulled off a great escape in the final to win for the first time in the 2015-16 World Series.
On home soil, the Kiwis needed a last-gasp try after the final hooter by Joe Webber to clinch a 24-21 victory over South Africa, triumphing in the event for the third year in a row, and fifth out of the last six.
Williams' late offload to Webber had helped the All Blacks come from behind to beat the Blitzboks 17-14 on Saturday, winning all three group matches, but he knocked on with his first touch of the final as South Africa led 14-0 and then 21-7.
Man of the match Akira Ioane -- once heralded as "the next Jonah Lomu"
-- reduced the deficit and made a try-saving tackle before his 18-year-old brother Rieko crossed twice while Rosko Specman -- who scored South Africa's scond try -- was in the sin bin.
Webber then dived over the line to win it after big defense at the other end by replacement Regan Ware.
"I'm privileged to be playing with such great players," said Williams, whose error had allowed Seabelo Senatla to score South Africa's third try.
"I've got a lot to work on and it's a learning curve, but I'm just glad to be doing it with these guys."
He wrote on his Twitter page that "Man I got that 7s bug now can't wait for Sydney, Gotta keep playing and learning" -- and told reporters that he found the game "very fast, very tough on the lungs."
Williams is one of several union stars hoping to win a place at the Olympics as sevens makes its debut in Rio in August.
The All Blacks, who have won 12 of the 16 titles since the series began in 1999, made a poor start to the 2015-16 campaign, losing in the Dubai semis and then the quarterfinals in Cape Town.
Victory in Wellington has lifted Gordon Tietjens' team into third place overall, with South Africa leading Fiji by two points ahead of next weekend's round in Australia.
"All week we talked about how we needed a lot of heart and a lot of ticker," NZ captain Tim Mikkleson said.
"Liam Messam came back from Japan and talked about putting the pride back in the jersey after the last couple of tournaments, and that's what we did. We talked about securing the kickoffs, and we bumbled a few and put ourselves under pressure, but we knew if we could keep the ball in hand we could win."