Then, in 2014, he was selected in the 14th round of the Major League Baseball draft by the Houston Astros.
After spending a few years in the team's system in the minor leagues, the 26-year-old has signed to play for the Auckland Tuatara in their inaugural Australian Baseball League season.
Tanielu will join the Tuatara for the second half of their campaign, starting with their series against the Adelaide Bite in mid-December.
For someone who has not travelled further from the United States than Mexico, playing in Australia was an opportunity he never expected.
"I can't believe I'm going to be in Australia," he said. "When [Baseball New Zealand chief executive Ryan Flynn] reached out, I wanted to do it, I just didn't know if I was going to be able to do it, but Ryan and the team worked hard to reel me in and make it worth my while. They've been nothing but good to me, so why not go back and help try to kick-start the Auckland Tuatara?"
Flynn told the Weekend Herald Tanielu was an exciting prospect.
"Nick is a special, special baseball player. He's right on the cusp of the Major League right now, which is really exciting.
"We hope to develop a long-term relationship with Nick as he makes the majors and wants to come back and reconnect with his Samoan heritage and family. We see him being a big part of the Tuatara and New Zealand baseball for many years to come, no matter how successful he becomes. He's a great guy, he's worked his way out of some difficult situations as a young man to the point where he's a world-class baseball player.
"I see him being an impact player in this league on day one. It's just a win-win-win situation for us getting this over the line."
With the Tuatara playing only three of their five home series in New Zealand this season, Tanielu won't get the chance to perform in Auckland, but was hopeful he would visit at the end of the season.
Since starting his career with the Astros, Tanielu said he had learnt how to better use his power and had developed better pitch recognition thanks to the coaches he's worked with. He's worked his way up through the organisation, and finished the 2018 season playing in the top level of Minor League Baseball.
On the cusp of the majors, Tanielu's knows his road to the top is clogged. The Astros infield is loaded with talent, including 2017 American League MVP Jose Altuve at second base, 2017 All-Star short-stop Carlos Correa and 2018 breakout star Alex Bregman at third base.
"It's tough," Tanielu said. "You go in every season knowing how great the Astros are and how good of a job they've done in the sense of getting all these superstars in the infield and outfield. So it's tough but you've just got to keep your head down and not worry about that, you can only worry about stuff you can control. My performance is in my control, so I can only worry about myself, worry about my teammates that I play with in the minor leagues and just get with my coaches there and try to better myself so I can help that Houston Astros team out when my time is called."
Tuatara coach Steve Mintz said Tanielu would be an important signing for the team who will come into the league built to compete for the title from opening day.
"He's a real good player. I think once he gets here, he'll be one of the better players in the league for sure.
"I think we've done a good job [with the roster]. Ryan [Flynn] has done a good job of finding some good Asian players and the people we have from New Zealand, too ... I think we'll be able to put together a pretty good team."
