Jayson Tatum was already a proven winner before last season.

In Tatum’s first six seasons, no NBA player won more games with one team than he did. Tatum played in 334 wins with the Boston Celtics over that span, including playoffs. He was a five-time All-Star, a legitimate MVP candidate, a four-time All-NBA pick, even an Olympic gold medalist.

He just wasn’t a champion.

“I had to listen to all the (stuff) that people said about me,” Tatum said.

That’s all in the past now. The Celtics are champions, coach Joe Mazzulla leading them to that crown, and when the season starts tonight in Boston — where last season ended — Tatum doesn’t seem to be considering it the start of a title defense. He’s looking at it as the start of a chase for a 19th title, and according to BetMGM Sportsbook, the Celtics are the favorites to claim the 2025 championship.

“It was never just about trying to just win one,” said Tatum, who added a second Olympic gold to his collection this summer. “Now you get to be mentioned with — at least be in the same room with — the other Celtics great teams, great players. All the guys that I looked up to growing up at least won one championship. Now it’s just a conversation of: ‘How great are you trying to be? What room or what tier are you trying to be mentioned in when it’s all said and done?’”

That journey starts with ring night in Boston, where the Celtics take on New York in the first game of a doubleheader to formally open the league’s 79th season. The nightcap is Minnesota at the Los Angeles Lakers, a game that will see LeBron James tie Vince Carter by playing in a 22nd NBA season — and potentially the first official game where a father and son are teammates, with Bronny James entering his rookie season.

There will be challengers to a Boston repeat, and a lot of them. New York (adding Mikal Bridges and Karl-Anthony Towns) and Philadelphia (adding Paul George) loaded up to try to supplant Boston atop the Eastern Conference. And there are rising teams in the East as well, like the Paolo Banchero-led Orlando Magic and Donovan Mitchell-led Cleveland Cavaliers — who made Round 2 of the playoffs last season.

And the Western Conference also has several contenders.

BetMGM has Oklahoma City — the No. 1 seed in the West last season, led by MVP hopeful Shai Gilgeous-Alexander — as the narrow favorite to win that side of the league, with 2023 NBA champion Denver, reigning West champion Dallas and a Minnesota team that went to the West finals a season ago all in the mix.

“You have to be careful with expectations put on outcomes,” Thunder forward Chet Holmgren said. “Around here we really emphasize putting expectations on processes, how we show up every day, how we go about our work, what we do, and the attention of detail that we do it to. That’s what we’re really focused on.”

The West is just loaded. But these Celtics — who return virtually intact from a year ago — know what it takes to be the last team standing.

“Boston can say whatever they want to say. They’ve earned it. They beat all of us and they were crowned,” Miami coach Erik Spoelstra said. “So, they can feel however they want to feel going into this season. With that said, (they) still have to earn it. But it’s a new season, new year. There’ll be a bunch of teams that are gunning for that title.”

Key dates to know >> Some notable events this season:

• Nov. 4: All 30 teams will be in action, with all start times staggered 15 minutes apart.

• Nov. 12-Dec. 17: The NBA Cup is back for a second season, with the semifinals on Dec. 14 in Las Vegas and the title game there three days later. The Lakers are the defending champions.

• Dec. 25: The Christmas games are San Antonio at New York, Minnesota at Dallas, Philadelphia at Boston, Lakers at Warriors and Denver at Phoenix.

• Jan. 23 and 25: Reigning rookie of the year Victor Wembanyama returns to Paris, with San Antonio taking on Indiana in two games there.

• Feb. 6: The trade deadline.

• Feb. 16: The NBA All-Star Game takes place in San Francisco.

• April 11 and 13: The last two game days of the regular season, with all 30 teams in action both days.

• April 15-18: Play-in tournament, followed by the playoff openers on April 19.