Vettel was coming off the back of his fourth world championship win in what was a devastatingly dominant campaign.
It was a daunting prospect for the fresh-faced Ricciardo, who learned a lot from the German that year.
“It was very respectful,” he said of their working relationship.
“Obviously I saw a little bit of the Mark/Seb rivalry, but at that time I was no longer Reserve Driver, I was more competing on the track at Toro Rosso, so I wasn't really in know.
“It was more just what you've seen maybe on the podium, or in the media.
“I didn't really know how to read [it] and I thought ‘okay, maybe the relationship might be tense'.
“But, deep down, I wasn't really expecting it to be tense. I thought, ‘okay, that's their thing, doesn't mean it's going to be my thing.'
“Up until that point, he was the most respective team-mate I had.
“We would battle, even like Monza – Monza I did that kind of switchback pass on him, sold him the dummy, and I feel that the time that was one of the first dummies to be sold.
“You do that on your team-mate, doesn't always feel that nice, but I remember after the race he came up, shook my hand, [and] said nice move.
“I didn't expect that; I probably wouldn't have done that at that time in my career – I was probably too much of a sore loser or whatever!
“But I remember when he came up to me, then I was like, yeah, you've got to respect that.
“That wasn't the only time [something like that happened], but that was a significant moment.”
Though they spent only a season together as team-mates, there were a number of lessons Ricciardo took away from their partnerships, while his respect for his former colleague runs deep.
“Record aside, one of the best to ever do it,” Ricciardo ventured when asked his opinion of Vettel.
“As a driver, it's not just about setting a quick lap, it's about how you work with the team around you, how you push your team.
“That was the first thing I noticed when I worked with him.
“He was very direct, very firm. For me, being probably a bit more of a nice guy, at times I was like ‘oh, that was pretty harsh', but actually it wasn't.
“It was never in an aggressive way, it was just as I said; direct and firm.
“But the message got put across and actually everyone was like ‘yeah, this kid wants that, he cares, he's showing the right intent'.
“So it actually drove a really good energy around the people that were working with him, so that was really cool to see.”
He then moved on to Aston Martin, where he stood on the podium for the final time at the 2021 Azerbaijan Grand prix.
However, in his latter years, he became outspoken on a range of topics, from the environment to diversity and equality, winning over many of his former critics in the process.
“As a human, he's honestly blossomed,” Ricciardo said.
“You don't grow a good heart overnight, I think he's always had a good heart, but as a competitor, it's hard to be vulnerable and to show that side.
“I think, just through time in the sport, a bit of growth, he's really blossomed now as a human and [is] very compassionate.
“Amongst us drivers as well he's very open and honest.
” I respected him as, obviously back then, as a team-mate, but now just as an individual, yeah, can certainly call him like a friend and someone I look up to.”
Vettel retired from Formula 1 following the Abu Dhabi Grand Prix last month, while Ricciardo has taken something of a sabbatical by rejoining Red Bull as Third Driver for 2023.