And, two years on, he has been able to reflect on an incredible progression that has seen him become first-choice hooker at cinch Stadium at Franklin's Gardens.
Back in 2019, Matavesi arrived and was immediately propelled into a Champions Cup clash with Leinster in Dublin.
It didn't end well as Saints were systematically demolished, losing 50-21 on a tough night.
But the team now appear to be in decent shape ahead of a first Champions Cup fixture of the current campaign, against another European giant, Racing 92, on Friday night.
And Matavesi is certainly in a much better situation that he was when he arrived at Saints two years ago.
"If you're playing, it's always nice and it's the best job in the world," said the ever-smiling 29-year-old.
"When you're not in and around it, it's tough, but for me personally I'm really happy.
"I think someone's going to give me a pinch and tell me to wake up.
"I'm really happy with my place in the team and having a bit more to do in meetings and things like that.
"I'm really happy!"
And Matavesi took some time to look back on that debut against Leinster and how things have gone for him since.
"It was my first appearance and to go there against a team at the peak of its powers in a packed Aviva, it was tough.
"But since the start of this season, it's been good for me.
"It's taken time.
"I never thought it was going to be easy but getting a run of games and getting that trust has been unbelievable for me.
"It allows you to get confidence and show what you can do more.
"I feel like I've been given free rein on things, which is nice."
Matavesi spent the autumn with his country as he featured in all of Fiji's matches.
And that international experience only whetted his appetite before returning to Saints, who he has helped to secure bonus-point wins in each of their past two games.
"Seasons are so long and with Fiji we play six games a year so when you get to go away it's a different environment and different people," said Matavesi, who has scored four tries in 35 appearances for Saints.
"It doesn't refresh you because I pretty much played three sets of 80 minutes but to go away and come back here, it makes you more hungry.
"We've come off two big wins against Bristol and Bath and games don't get much bigger than the one this week with Racing coming here.
"It's really exciting.
"We've got a massive game coming up and it's going to be a massive challenge."
One of Matavesi's autumn appearances for Fiji came in Cardiff, where he delivered a hugely impressive showing in defeat to Dan Biggar's Wales.
Api Ratuniyarawa also started that game, and several Saints players hired a mini-van to go and watch their team-mates in action.
"It's awesome and it shows how tight we are as a squad," Matavesi said.
"All the Academy boys did the same for Kayde (Sylvester) when he made his first appearance back from injury for Loughborough.
"It shows as a squad how everyone's tight and you can see on matchday that it works."
Saints will now look to put together a true team performance when they host a star-studded Racing team this week.
And Matavesi said: "We got a few things we got wrong against Bath last week and if we do what we did last week against this team, we'll get punished.
"But this is going to be different and we've got to put our spin on them.
"It's going to be different to what they've faced previously and we know the team that can put their game on the pitch for the longest period will win."