"We can't panic. It's only one game," he told reporters, via Chris Forsberg of ESPN.com. "One game. They took care of business and we just gotta take care of business in Game 2."
He continued: "I believe in these guys. We're not scared of Cleveland. They're not the Monstars. They're not on Space Jam. They lace up their shoes just like us. They just happened to play better than us in Game 1. We just gotta protect home court in Game 2 and get the win."
Recovering against LeBron James and the defending champions isn't something any team has been able to do this postseason, however. The Cavs are 9-0 in this year's playoffs and now 4-1 against the Celtics overall in the 2016-17 campaign.
Still, doubting Thomas has been a fool's errand this year. The diminutive guard established himself as one of the game's most dangerous offensive weapons this season, averaging 28.9 points and 5.9 assists per game.
This postseason, he's led the Celtics to the Eastern Conference finals, all while dealing with the death of his sister and a tooth that was knocked out against the Wizards. But Thomas and the Celtics aren't done yet, as he said on Thursday, per Forsberg:
"We're not just happy to be here. We want to win this series. And that's what we're trying to do. We want to let everybody in this world know that we're for real and that we're one of the top teams in the NBA. With this series, we gotta go out and show the world. Everybody knows that everybody is counting us out. And we've been there before, though. It's nothing new for us."
It's nothing new for James and the Cavaliers either. So the Celtics, no matter how confident they remain, still face a daunting task.