Coach Brad Stevens has lost five of the nine players who were in the Celtics’ main rotation a season ago. But he says of the 2019-20 squad, “I really like the guys that are in our gym right now.” Nick Wass/Associated Press

PLYMOUTH, Mass. — There was an overflow of optimism at this time last year when it came to the Boston Celtics’ prospects for the 2018-19 season.

A team that went to Game 7 of the Eastern Conference finals was adding Kyrie Irving and Gordon Hayward, who had been sidelined with injuries, making the Celtics the clear-cut preseason favorite to win the Eastern Conference title.

But then it all fell apart for the Celtics as they couldn’t even win 50 games in the regular season and were bounced from the playoffs in the second round, losing in five games to the Milwaukee Bucks.

Turmoil was a running theme throughout the season, and an unhappy Kyrie Irving caused disruptions along the way.

Four and a half months after the ugly ending to the season last May 8 in Milwaukee, the Celtics are preparing to open training camp on Tuesday and putting the failure of a year ago in the rearview mirror.

Coach Brad Stevens made an appearance at the Celtics Shamrock Foundation’s 12th annual Teeing Up For Kids Golf Tournament earlier this week and addressed the recent past and upcoming season.

Stevens is about to enter his seventh year with the Celtics and took a lot of the blame with what went wrong last season when a team with such high hopes lacked chemistry.

“My care is that we play with great effort and togetherness. That is it,” said Stevens of the 2019-20 season that begins Oct. 23 in Philadelphia against the 76ers. “That’s what we’re looking for. That’s what we want to be. All the technical basketball plays, that stuff will figure itself out. I feel like we’re in a good foundation there, but we’ve got to play like a Boston team should.

“I thought we did at times (play with effort and together last season). I didn’t think we were as good as maybe a couple of years before. But that’s not brain surgery. I realize every time we say that, that’s the headline, but at the end of the day, this team has done a good job of flipping the page, moving forward and focusing on itself. I really like the guys that are in our gym right now.”

Five of the nine players in the main rotation from a year ago – Irving, Al Horford, Marcus Morris, Terry Rozier and Aron Baynes – are gone and the marquee addition is All-Star guard Kemba Walker.

The Celtics appear to lack interior defense and rebounding, so it is going to be interesting to see how the puzzle comes together.

Stevens spent part of the offseason looking for ways to avoid the way things collapsed last season and has moved on to making all the new pieces fit.

“We didn’t play as well as we had hoped,” Stevens said. “I’ve said this many times that that starts with me. It was my job of doing a better job of getting ready.

“I think we’ll be better as far as the important stuff and we’ll find out as good we can be as time goes on.”

Walker, Jayson Tatum, Jaylen Brown and Marcus Smart are back from China where they played for the United States in the World Cup.

Stevens said that everyone on the roster, including first-round pick Romeo Langford, will be ready to go for the first practice on Oct. 1. A number of players have been at the practice facility in Boston working out for several weeks.

“I just think there’s a lot to be excited about,” Stevens said. “We have a lot of work to do. We’ll get to that next week. I think we have a lot of guys who are ready to practice. There’s a good excitement, but I think all 30 teams have that.

“I think our guys are excited and ready to get after it.

“We have so many new guys. It’s just a different scenario, a different feel, a different group altogether.”

The Celtics are not going into this season as the favorite to emerge from the Eastern Conference, but there is hope that improved chemistry and the growth of young players can add up to a better experience.

“(There’s) a lot of positive vibes,” owner Wyc Grousbeck said. “I think Brad seems to be confident that he can take this group and we can go somewhere.”