This was an unusual offseason for the champion Celtics.

Typically, when a team wins an NBA title, it loses at least a few important pieces. Role players leave for richer contracts and more minutes elsewhere. Trades are made to clear salary cap space. Aging veterans retire.

Not Boston.

In the weeks that followed their 18th championship, the Celtics proceeded to retain every player of consequence from their 2023-24 roster. They re-signed reserves Sam Hauser, Luke Kornet, Xavier Tillman and Neemias Queta, re-upped G Leaguers JD Davison and Drew Peterson on two-way contracts, and extended starters Jayson Tatum and Derrick White, who both were set to enter contract years.

The only players from Boston’s playoff roster who won’t return are forward Oshae Brissett and guard Svi Mykhailiuk, who ranked 12th and 13th in minutes played per game last season and weren’t part of Joe Mazzulla’s postseason rotation. The team’s lone newcomers are 2024 draft picks Baylor Scheierman and Anton Watson.

Starting guard Jrue Holiday, the only member of last year’s Celtics squad who’d previously won an NBA championship, said that rare continuity will give Boston a “head start” over the rest of the field once the 2025-26 season begins in October.

“I think it’s going to help a lot,” Holiday said Wednesday at the grand opening of a new Raising Cane’s restaurant in Downtown Crossing. “It’s always hard to win one, but then to win back-to-back is even harder. So I think just kind of getting a head start on other teams, possibly, where we have the continuity and the goal that we wanted for the end of the season — it ended up happening for us, but to be able to go into the next season locked in and doing the same thing (will help).”

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After Holiday won it all with Milwaukee in 2021, the Bucks lost playoff starter P.J. Tucker and backup guard Bryn Forbes the following offseason. They were bounced in the Eastern Conference semifinals in 2022.

Repeating in the NBA has become exceedingly difficult in recent years. The last team to win back-to-back titles was the Golden State Warriors in 2017 and ’18. In the six years since, there have been six different champions, with no title-winner even reaching the conference finals the next season.

Holiday will play a vital role in Boston’s bid to reverse that trend. The trades for him and center Kristaps Porzingis last offseason helped put the Celtics over the top after a half-decade of near misses, and Holiday signed a contract extension in April that ties him to the C’s through at least 2027, with a player option for 2027-28.

The 34-year-old averaged 12.5 points, 5.4 rebounds and 4.8 assists over 69 appearances in his first season with the Celtics and earned All-Defense honors for the sixth time in his career. He and teammate Derrick White both were second-team selections.

The Celtics will open their 2024-25 season Oct. 22 against the New York Knicks at TD Garden.