For the first time this season, the Celtics took the court Tuesday night without both of their All-Star centerpieces. Boston downgraded Jayson Tatum (right knee tendinopathy) from questionable to out ahead of their matchup with the Brooklyn Nets at TD Garden. He joined co-star Jaylen Brown, who was ruled out a day earlier with a right knee posterior impingement. The last time the Celtics played a game without Tatum or Brown active was their 2023-24 regular-season finale, when head coach Joe Mazzulla rested his starters with the No. 1 seed secured. Boston’s seeding for the upcoming postseason is not yet solidified, but it would take a stunning collapse to move it from its current spot as the No. 2 team in the Eastern Conference. The Celtics entered Tuesday 7 1/2 games back of first-place Cleveland and 5 1/2 ahead of third-place New York with 14 games remaining. Mazzulla has said winning each game still is the team’s priority, but he’s already begun dialing back his top players’ workloads. Since the NBA All-Star break last month, the Celtics have had their preferred starting five active for just two of their 14 games. A large reason for that was the illness that sidelined Kristaps Porzingis for eight straight contests — he returned Saturday night and immediately impressed in a 115-113 road win over Brooklyn — but Boston also played five games without Jrue Holiday, four without Brown, three without Tatum and one without Derrick White. Rotation reserves Sam Hauser, Luke Kornet and Al Horford missed one, two and four games during that stretch, respectively. With the Celtics’ playoff seeding unlikely to change over the final three-plus weeks of the regular season, Mazzulla will have little incentive to overburden his starters. Finding the proper balance between rest/injury prevention and ensuring players are in rhythm and free of rust will be key for Mazzulla and his staff. Porzingis’ usage will be especially interesting to monitor. The 7-foot-2 center is the most fragile of Boston’s core players and has proven he can quickly make an impact after a prolonged layoff (see: Saturday’s game in Brooklyn; last year’s NBA Finals). That said, he’s played in less than half of the Celtics’ games this season and has seen even less action with their full starting lineup, which struggled for several weeks after his November return from offseason leg surgery and still owns a negative net rating this season (-1.6). 3-point chase Three different Celtics players are making a run at Isaiah Thomas’ franchise record for made threes in a season (245 in 2016-17). Tatum entered Tuesday’s game with 227, followed closely by White with 225 and Payton Pritchard with 220. All three are on pace to break it — each is averaging more than three 3-point makes per game — but whether they’ll do so could depend in part on how Mazzulla plans to deploy Tatum and White down the stretch. It would not be a major surprise to see Pritchard top that list by season’s end, as he’s the least likely of the three to receive any designated rest days. Pritchard already set the NBA record for most made threes off the bench in a season, unseating Wayne Ellington (218 in 2017-18) during Saturday’s win over the Nets. Last season, all five of Pritchard’s starts and his six highest minute totals came in mid-to-late March or April as Mazzulla lightened his starters’ workloads ahead of the playoffs. And speaking of 3-point records, the Celtics still are on track to smash the 2022-23 Golden State Warriors’ NBA mark for made threes in a season despite making those shots at a substantially lower rate than they did last season. Boston entered Tuesday shooting 36.9% from deep as a team (seventh-best in the league), down from 38.8% a year ago (second-best).