Jalen Johnson of the Atlanta Hawks blocks a shot by Jaylen Brown of the Boston Celtics during Saturday night’s game at Boston. The Celtics lost 119-115 in overtime and Brown had shots blocked eight times. Robert F. Bukaty/Associated Press

Leadership. Every successful team needs it. The Celtics and Bruins returned to work Monday, hoping to find it from their top players. They missed it over the weekend, especially during each team’s overtime loss Saturday.

At TD Garden in Boston, the Celtics had a comfortable 10-point lead in the fourth quarter against the Atlanta Hawks, a team that was just two games over .500. Champions need to close those games out. Instead the Celtics stumbled through the sloppy final minutes, with Jayson Tatum and Jaylen Brown missing shot after shot in a 119-115 loss in overtime.

Brown, who had eight shots blocked against Atlanta, is having one of his worst shooting seasons. He is also avoiding the media after games. When Brown wasn’t chosen to play for Team USA in the Olympics, fans hoped he would use that motivation to lead the Celtics to a second straight NBA title.

It’s not happening. He has the lowest field-goal and 3-point percentages of his career. He is also struggling defensively, at least by his standards. His Defensive Win Shares, an estimate of the number of wins a player contributes to his team via defense, is his lowest since his rookie season. His 1.5 DWS is less than half what it was last year.

After Saturday’s loss, coach Joe Mazzulla stressed that there was “no fear” in the Celtics’ locker room and he continues to believe in his team. The players have the talent to repeat this spring, but Brown will have to step up and lead like he did in the playoffs last season.

In Ottawa, the Bruins had an equally brutal collapse. Leading by two goals with less than five minutes remaining, Boston fell apart before losing to the Senators 6-5 in a shootout. With the win, Ottawa moved ahead of Boston in the standings even though they played two fewer games.

The late-game collapse was the latest in a season full of mystifying losses for the Bruins. Even more mystifying was the absence of captain Brad Marchand during the five-minute overtime when the Bruins were outshot, 3-1.

Boston’s Brad Marchand tries to get his stick on the puck as it bounces near the mask of Senators goaltender Leevi Merilainen on Saturday in Ottawa, Ontario. Marchand did not play in overtime and Boston lost 6-5 in a shootout. Justin Tang/The Canadian Press via AP

Coach Joe Sacco called Marchand’s absence an “in-game decision.” He didn’t expound a day later after practice, so fans are left wondering how the team’s second-leading scorer stays on the bench with a vital point on the line.

Back in November, then-coach Jim Montgomery benched leading scorer David Pastrnak for the entire third period of a win over Seattle.

“Coach’s decision,” Montgomery said at the time. Before the end of the month, Montgomery was making those decisions for another team.

Are the Bruins a dysfunctional group? WEEI’s Rich Keefe speculated on the air that Marchand and Pastrnak didn’t get along, calling the team’s dressing room “a disaster.” Marchand quickly and publicly refuted the report.

Yet we’ve seen each of these players, both leaders of this team, benched at crucial moments this season. Even if there isn’t a riff, there is a problem with this roster.

Now the Bruins are on the outside looking in on the playoff pack. Team president Cam Neely said he’s looking at two paths forward, acknowledging the team may have to trade veterans to rebuild.

The Celtics aren’t thinking about rebuilding, but if their top players don’t start leading the way soon, this will be a disappointing spring for both tenants at TD Garden.

Tom Caron is a studio host for the Red Sox broadcast on NESN.