Robert Williams III — Celtics can’t keep coming from behind

BOSTON — The Boston Celtics have made a habit out of responding to adversity over the past two postseasons.

Celtics center Robert Williams III said he expects his team to do so again when the Eastern Conference finals resume against the Miami Heat with Game 2 on Friday night here at TD Garden, but he said Boston’s insistence on putting itself in such positions is eventually going to come back to haunt the team.

“There’s no doubt in my mind that we’ll come out ready to play in Game 2,” Williams said after Boston’s practice Thursday afternoon. “But the problem is we can’t keep relying on that.

“We can’t rely on our backs being against the wall. There’s no time for it. We have to fix it.”

After dropping Game 1 of this series to the Heat on Wednesday, the Celtics will be looking to improve on their 4-1 record in these playoffs coming off of a loss, and an 11-3 record in those situations over the past two playoffs.

But that ability to bounce back — and that it has had to happen so regularly, as Williams pointed out — goes back to Boston’s maddening level of inconsistency over the course of these past two playoffs. Nothing signifies that trend more than the way the Celtics have played at home.

Including Wednesday’s Game 1 loss, the Celtics are now 10-10 at TD Garden over the past two postseasons. They were 6-6 here a year ago, including losing Game 6 of the NBA Finals to the Golden State Warriors to end last season, and are now 4-4 at TD Garden in these playoffs.

“There were moments where we executed, there’s moments where we played well, and then there were moments where we didn’t,” Celtics coach Joe Mazzulla said.

“This series is a test of discipline, it’s a test of mentality, and we’ve got to be extremely detailed in our effort and our consistency.”

The only thing consistent about the Celitcs, however, is their lack of consistency. That was once again on display in Game 1, after Boston controlled the run of play through the first 24 minutes — dominating the paint, taking care of the ball and jumping out to a nine-point halftime lead — before allowing Miami to explode for 46 points in the third quarter alone to turn the game on its head and allow the Heat to steal back home-court.

Not surprisingly, most of the focus of Thursday’s film session was on what happened in those 12 minutes and what Boston needs to correct moving forward.

“It looked exactly like it looked last night,” Williams said. “It was a lot of stuff you don’t want to see.”

“It was pretty much what I thought,” Joe Mazzulla said.

There was little that went right. Like after the game, the Celitcs talked a lot about spacing issues offensively gumming things up. The defense was clearly a problem, given the Heat nearly matched their first-half total over the course of 12 minutes.

In specifics, though, Mazzulla was asked about two rotation decisions from Game 1: starting the double-big lineup of Williams and Al Horford together, and then playing guard Payton Pritchard over forward Grant Williams.

The Robert Williams-Al Horford pairing — as part of a starting lineup with Jayson Tatum, Jaylen Brown and Marcus Smart — was one of the NBA’s most dominant lineups last season under former coach Ime Udoka. This season, it barely saw the court, as Williams spent the first couple of months of the season rehabbing from September knee surgery, and then Mazzulla tended to stick to more offensively oriented lineups featuring more speed, spacing and shooting.

But Mazzulla went back to that group in Game 6 of the Philadelphia series, a move that helped flip it in Boston’s favor and allow the Celtics to reach this point. In Game 1 against Miami, however, Williams was a team-worst minus-14 in 26 minutes, and that five-man unit was outscored by 10 points in nine minutes together.

“That’s a good question,” Mazzulla said, when asked what he thought of that grouping in the first game. “I thought each lineup presented things that did well. I thought Rob was really good, 6-6, got offensive rebounds, really kind of got us going at the same time. We just have to be more consistent regardless of the lineup. So we’ve developed an identity this year to play a bunch of different ways, and so we can’t just look at it as it’s this way versus that way.

“We have a lot of depth … and so we just have to be able to use that and flex into that, and when we go into those different lineups at different times, we got to maintain our spacing and understand what we’re doing when with those lineups out there.”

Part of that versatility was also represented in Mazzulla going to Pritchard for 12 minutes in Game 1 and continuing to leave Grant Williams — an essential part of Boston’s playoff rotation a year ago — off the court this time around.

After playing in every playoff game last year, starting several and playing over 27 minutes per game in Boston’s run to the Finals, Williams has played in only nine of Boston’s 14 playoff games this time around, and is averaging 12.9 minutes per night.

Mazzulla — who also went to Pritchard in Game 5 against Philadelphia — said he went with Pritchard against the Heat because he liked his shooting, playmaking and pick-and-roll defensive ability.

“We have a plan to use the depth we need in order to give us the lineups we think can really help us, and obviously, in the playoffs when minutes are expanding, you look to play seven or eight guys throughout,” Mazzulla said. “Grant is always gonna be ready, and we’ve built a lot of versatility in our lineup where we can go a lot of different ways. We trust that anybody we call on will be ready.”