To understand the breadth of what they accomplished in Game 3 — and yet we understand the accomplishment means little unless they follow with another win Sunday — you have to understand how low the Boston Celtics had been after Game 2.

Doc Rivers spent the day between the two contests telling reporters his team actually gained confidence from the crushing, 115-111 overtime defeat. But Keyon Dooling, who normally toes the company line, had to disagree.

“It was a disheartening game for us,” the veteran guard explained, “but our response is always going to be grit. If you’ve been around this team, you understand we don’t have any lay-down in us.”

The Game 2 loss had to hurt. How could it not? With a chance to even the series and steal home court advantage, the Celtics wasted 44 points from Rajon Rondo and blew a 15-point first-half lead. They held Dwyane Wade scoreless for the first 23 minutes and shot 49.4 percent from the field themselves — and lost.

“You digest it, you think about it, you watch film and go through practice. It dominates your thoughts. What can you do better? This is our job, this is our livelihood, so we want to try and maximize our potential,” said Dooling. But as much as the loss stung like alcohol on an open wound, Dooling knew how the Celtics would respond. “We’re a team that is very, very, very gritty. We continue to hang in there. Tonight we came out and treated it like a game 7. We wanted to leave everything on the court.”

Leave everything on the court, sure. The Celtics had no choice.

“Desperation game, to be honest,” described Kevin Garnett. “And we played like it too. You don’t want to be down 3-0 to a team like this.”

You don’t want to be down 2-1 to a team like this, either. The Celtics are unfortunately stuck with that deficit, but made some changes Friday to help give them hope in the Eastern Conference Finals.

In Game 3, Doc Rivers still made several adjustments to give the Celtics decided advantages. With the Heat switching several ball screens on Rajon Rondo, the Celtics stopped running their bread and butter pick-and-pop and instead opted for a series of pick-and-rolls designed to isolate Garnett on the block against smaller defenders. When the Heat did not switch, the pick-and-roll was still a better option for Boston — even Miami’s tallest defenders, Joel Antony and Udonis Haslem, can’t handle Garnett inside. Miami likes to front the post, mostly out of necessity, and Rondo is capable of lofting passes with a perfect trajectory just outside the reach of defenders, like a quarterback might throw a jump ball for a tall wide receiver like Randy Moss. The result of the pick-and-roll focus was that the Celtics attempted fewer mid-range field goal attempts, 15, than they had all season.

Thousands of words have been written, here and elsewhere, discussing how Garnett’s move to center allowed him the ability to roam freely on the perimeter and in transition against slower defenders. But in the playoffs, he has been willing to play to his matchups — and the succession of mediocre big men opponents, from Jason Collins to Elton Brand to Joel Anthony, has dictated that Garnett operate on the interior.

For Garnett, more of a finesse player at heart, who had been reluctant to make the switch to center, the change probably hasn’t been natural. But it’s working.

Said Rivers, “Yeah, we have to keep the discipline in staying with it.  Listen, this is exhausting.  You get guys grabbing you and holding you, and you’re trying to roll and they’re fronting you.  It’s exhausting.  But I thought we made terrific passes in the first half.  Every time Kevin rolled.  One of the things we kept telling them at the end of the day, throw it up.  There’s nobody taller than him on the floor.  Throw it up in the air, Kevin will go get it.”

Rivers sometimes appears to make lineup decisions as if he pulls names out of a hat, which is why many might have regarded his insertion of Marquis Daniels into Game 3 as the random workings of a coach grasping for straws. But Rivers had a plan. Not only is Daniels physical and versatile enough to defend Miami’s small-ish power forwards or LeBron James while allowing Boston to go small, but he’s a talented cutter with a knack for getting behind the defense. Because of Miami’s tendency to swarm defensively, the Heat can be susceptible to backdoor cuts on occasions when they over-help. We saw how Avery Bradley used the Heat’s athleticism against them during the regular season with a procession of off-ball slashes, and Daniels similarly succeeded last night without ever having to touch the ball for more than a second or two at a time.

Daniels only played two combined minutes during the first two games of the series, but based on Rivers’ comments, the coach always thought Daniels could help against Miami.

“He told me the last two games, ‘Be ready.  You’re going to play tonight,” Daniels said. Of course, before Game 3 he hadn’t played any significant time in the series. But I suspect Rivers might have feared throwing a seldom-used player directly into the Eastern Conference Finals on the road. Back at home in the TD Garden, Rivers could trust his gut and called Daniels’ number.

NBA playoffs series are a chess match of adjustments. Rivers took a few of Miami’s pieces on Friday. But if Erik Spoelstra can respond well in Game 4, the Celtics are still one loss from falling into check.