"We had a game on Saturday against the Wellington provincial side and he played his first official game of sevens and certainly excelled.
"He's still got a lot to learn but we felt it was the right time to introduce him."
Tietjens held back from confirming exactly how much of a role Williams would play in the tournament, but expects him to enjoy some game time either off the bench or in the starting line-up.
"It's all about confidence, sevens. And playing in your own tournament in Wellington...I know that Sonny's quite nervous, but with that there's a lot of excitement," he said.
"He's gelled and settled in really well with the guys. It's an exciting team and there's certainly a place for someone with his skill-set to certainly utilise them in this All Blacks Sevens team."
Brothers Akira and Rieko Ioane, Hurricanes loose forward Ardie Savea and Glasgow Commonwealth Games reps Ben Lam and Kurt Baker have been named to make their international sevens returns.
Sam Dickson, Gillies Kaka, Augustine Pulu, Regan Ware, Joe Webber and captain Tim Mikkelson round out the squad.
The All Blacks Sevens will face Russia, Scotland and South Africa in pool play on Saturday.
New Zealand Sevens team: Kurt Baker, Sam Dickson, Akira Ioane, Rieko Ioane, Gillies Kaka, Ben Lam, Tim Mikkelson, Augustine Pulu, Ardie Savea, Regan Ware, Sonny Bill Williams, Joe Webber.