One week after wearing a Celtics hat to his team's first spring practice, and ensuring his assistants did too, Belichick opened his remarks to reporters Tuesday by saluting the newly crowned Eastern Conference champions.
"Another big series for the Celtics. Congratulations to the team, the staff, the organization. Great accomplishment," he said. "Look forward to seeing that play out."
Game 1 is Thursday night at Golden State (9 p.m. ET, ABC).
Asked what he has observed from the Celtics this season, Belichick said: "They've played great in the last two-thirds of the season and playoffs. Really consistent. They have a lot of good players. Played really good defense.
"They're tough, they hustle, play smart basketball. Pleasure to watch. Fun to watch."
Patriots safety Adrian Phillips, who was hoping for a Celtics-Mavericks NBA Finals matchup because of his ties to Texas, was among the Patriots players putting their support behind Boston on Tuesday.
Several Patriots have attended Celtics playoff games this year, including quarterback Mac Jones, receiver Kendrick Bourne, running back Damien Harris and tight end Jonnu Smith. Patriots owner Robert Kraft is also a regular at TD Garden.
Games 3 and 4 of the NBA Finals are scheduled to be played in Boston on June 8 and June 10. The Patriots will hold their mandatory minicamp June 7-9.
Belichick said connecting with other professional sports teams in Boston has been an enjoyable part of his experience as Patriots coach, all the way back to his first season (2000) with then-Celtics coach Rick Pitino.
"Some of those guys move on [but] it's good to stay in touch with them, even though they're in different organizations. Still going to pull for the home team. [But] the relationships there, they extend past the initial introduction."