Flores cited timing and progress from the first-round rookie as the primary reasons he felt comfortable making the switch.
"We feel like that's the best thing for the team," Flores said, according to NFL.com's Kevin Patra. "We feel like through practice and meetings and walkthroughs that he's ready, and that's how we're going to move going forward.
"I think he's gotten more comfortable. Accuracy, decision-making, all of those things have been good in practice. But again, practice is very different than a game. We're comfortable and confident that he'll be able to be competitive in those games when the time comes."
Tagovailoa replaces Ryan Fitzpatrick at quarterback. The veteran performed well across six starts - completing 70.1% of his passes for 1,535 yards, 10 touchdowns, and seven interceptions - but it was only a matter of time before Miami turned to the fifth overall pick in April's draft.
"Look, Fitz has been great," Flores said. "He's been great really for the last year and a half. I don't know if there's anybody who's been more instrumental in trying to instill a culture and embody a lot of things we're looking from a toughness, competitiveness, team-first ... He's made an impact on Tua (and) a lot of the players on this team. So I have a great respect for him, and that made this decision very tough.
"But at the end of the day, as a team, we felt like the best thing to do for our team now and moving forward was going with Tua. But I think Fitz and the way he handles himself and his impact on the team, it'll still be there. He's been a tremendous asset and leader for this team."
The Dolphins have a bye in Week 7, so Tagovailoa will make his first career start next week against the Los Angeles Rams.