BOSTON — The Miami Heat did not score their first basket until there was 3:22 left in the first quarter on Monday night, the longest period without a field goal to start a playoff game in almost three decades, according to ESPN.

It only got worse from there, the result of yet another bizarre game in this Eastern Conference finals series against the Boston Celtics. From game to game, like Forrest Gump’s box of chocolates, you don’t know what you’re going to get.

During Game 3 on Saturday night, the Heat went up 26 in the first half. In Game 4, it was the Celtics’ turn to go up 27 before halftime, despite missing their starting point guard, Marcus Smart, because of an ankle injury from the previous game. Most of the starters were out of the game for good by early in the final quarter.

Through the first four games, the series has been mostly a sequence of wild, uncharacteristic swings by both teams. On Monday, Boston led by 32 at one point before winning, 102-82. Neither team has been able to carry momentum into the next game, despite looking dominant for long stretches.

“It’s wild, right? I’m not really sure how to explain it,” Heat guard Victor Oladipo said.

The series is tied at two games all, but not because it has been especially competitive. Amazingly, the last time there was a lead change was in Game 2, in which the Celtics led by as many as 34. It was the only lead change of the game. Each team has apparently conveniently forgotten the tipoff time every other game. In three of the four games, a team has been leading by double digits at the end of the first quarter.

“It’s an inconsistent series from both teams at times, and it’s an odd one, honestly,” Celtics Coach Ime Udoka said.

It hasn’t been a question of being home or away, since each team has won a game on the road. Either the Celtics and Heat have been at their best or worst. There have been very few in-betweens.

“Sometimes when you have two really competitive teams, it doesn’t necessarily mean it’s going to be a one-point game,” Heat Coach Erik Spoelstra said. “It means that it can be flammable either way. Both teams are ignitable.”

He continued, “Both teams can really defend and get teams out of their comfort zone and distort a lot of things offensively, and that can fuel big runs on the other end.”

On Monday, the advantage belonged to Boston from the start. The Celtics were quicker to loose balls, more active in disrupting passing lanes and more coordinated in switches, limiting quality looks for Miami. They were more urgent in getting back on defense and rotating in the paint, not allowing the Heat to push for fast breaks as they did on Saturday. Boston’s defense was so effective that Miami shot only two 3-pointers in the opening quarter, limiting their chance at making up the deficit until it was too late. It was the exact kind of energy that Boston sorely missed in the first half of Game 3. Miami’s starters combined for 18 points.

What made the game even stranger is that the Celtics didn’t play well offensively. They were only 5 for 27 from 3 when they entered the fourth quarter up 24 points and the game was effectively over. They ended the game shooting 39.7 percent from the field, a percentage that would result in a loss on most nights, not a blowout win. They also won in spite of a poor game from guard Jaylen Brown, who shot 5 for 20 from the field for 12 points.

Miami, a team that likes to pride itself on its hustle culture, gave up 10 offensive rebounds in the first half. Heat center Bam Adebayo, who finally broke out for 31 points in Game 3, reverted back to being tentative, shooting the ball only twice in the first half. He finished with 9 points. In large part, this was because of the presence of Celtics center Robert Williams III, who missed Game 3 because of knee soreness. Williams, who was named to the All Defensive Second Team last week, made life difficult at the rim for Miami. He had 12 points and 9 rebounds in only 19 minutes.

“We shouldn’t have to get punched in the mouth to respond,” Williams said of the team’s poor starts in its losses.

Perhaps this game was inevitable. The Celtics have not lost two games in a row the entire postseason. In their semifinal matchup against the Milwaukee Bucks, Boston responded to letdowns with three strong performances. No one has been more indicative of the Celtics’ fortunes this postseason than their top player, Jayson Tatum — a Jekyll and Hyde superstar.

There are nights when Tatum looks like one of the best players in the league. Those nights are often coming off Boston defeats. Including Monday night’s 31-point performance, Tatum has averaged 32.6 points after the Celtics' losses during the postseason. He was aggressive in attacking the basket, getting to the line 16 times, more than any other game in this playoff run.

But when Tatum plays poorly, he looks more out of sorts than most superstars. His shoulders slump. He settles for difficult step-back jumpers, complains to referees and doesn’t get back as aggressively on defense. In Game 3 against the Bucks, Tatum had only 10 points and shot 4 of 19 from the field. On Saturday night, Tatum had a similar performance — scoring 10 points on 3-of-14 shooting.

“I think I do a really good job of sleeping it off, regardless if I have 10 points or 46 points,” Tatum said, adding, “I’m a big believer in you can’t change what happened.”

But the Heat may have a star problem of their own going forward in the series. For the second straight game, Jimmy Butler, their top playmaker, looked slow and lacked explosiveness. He missed the second half of Game 3 because of knee inflammation. On Monday, he didn’t look any better, missing almost all of his shots at the rim. He didn’t go to the free throw line once in 27 minutes, a blatant sign that something is off. He averaged eight foul shots a game in the regular season, among the best in the league. In Game 1 alone, he had 18.

Asked about his knee, Butler said: “I’m straight. No excuse for how I played tonight. It don’t got nothing to do with my knee. I’ve just got to be better. I will be better. I’m not too worried about it.”

Miami was already prone to offensive droughts. But without Butler at peak effectiveness, the Heat will have a difficult time scoring against one of the best defenses in the N.B.A. His absence was felt on Saturday, when the Heat nearly blew their 26-point lead in that second half. His ability to penetrate and pass creates shots for others.

But maybe the Heat will be fine either way. There hasn’t been much rhyme or reason for why the teams have alternated unleashing torrents on each other on a given night. And Game 5 at home, if this series is any indication, is Miami’s turn.

“We’ve proven that we can do it,” Spoelstra said. “The margin for error for either team — whatever they have done to us, we can do to them. None of us are happy about what happened tonight.”