MIAMI — Less than three minutes into Saturday’s second quarter, the Miami Heat already trailed by 17 points and starved for any offensive rhythm.

Caleb Martin — the unlikely hero of last year’s East Conference Finals — found himself with the ball in the corner and an open look at a 3-point shot.

Martin flinched, dribbled left and looked like he was about to pass the ball back to Tyler Herro, but he decided to keep dribbling. By the time Martin reached the other side of the court and finally let the ball go, his intended target, Jaime Jaquez Jr., left the corner to run toward the hoop.

Martin’s pass fell helplessly at the feet of Duncan Robinson, who was sitting on the Heat bench.

If one play summed up the Heat’s 104-84 Game 3 loss to the Celtics, that was it.

A few days after eighth-seeded Miami made a franchise playoff-record 23 3-pointers on 43 attempts with determined conviction to beat Boston at its own game, the Heat played all out of sorts and looked like a team badly missing its top-two assist leaders in Jimmy Butler and Terry Rozier.

The Celtics had a lot to do with that. Coach Joe Mazzulla dialed up more pressure on Miami’s primary ball distributors to speed up the Heat’s offense. But there were still open looks such as the one Martin passed on, which led Miami to play like the team that got beat by 20 in the series opener.

“Honestly, we just made mistake after mistake on offense — not communicating, throwing the ball away, turnovers that shouldn’t happen in the playoffs,” said Bam Adebayo, who led Miami with 20 points, nine rebounds and three assists on a night the Heat trailed by as many as 29 points and never cut the deficit below 18 in the second half.

“I don’t think we really brought that dog tonight like we did in Game 2, when we set the tone from the jump,” he continued. “Obviously, when you don’t have that type of dog mentality, you can get blown out by 20. Next time, I’m gonna yell at my teammates to shoot the ball.”

Martin, who scored five points on only four shot attempts in 38 minutes Saturday, owned his end of the bad night.

“There were some times I passed up (shots),” he said. “I was trying to get the ball moving a little bit more, being a little bit less aggressive and letting it go. That’s on me. I’ve got to be aggressive.”

Herro, who had a career-high and team road playoff-record 14 assists in Game 2, had two assists and four turnovers and finished with 15 points 5-of-16 shooting, including a 3-of-9 mark from beyond the arc. Not only did the Celtics tighten up their coverage on the perimeter — they forced Herro into taking five more two-point shots than he did in Game 2.

“I have to do a better job of creating and making the right decisions when I get into the paint. Same with Bam,” Herro said .”Our guys just have to shoot the ball. They are open. They have to let it ride and let it go.

“We don’t have a quote-unquote ‘point guard’ right now. But we have a bunch of guys that can get us into offense. So, I think that they’re gonna continue to try to bring that pressure so that we can kind of get sped up and make the decisions harder for us. I also feel like we can do a little bit of the same to them, kind of get into them, speed up the ball a little bit and kind of force them into mistakes.”

The problem Erik Spoelstra faces is he just doesn’t have very many options to turn to for offensive help.

Butler, Miami’s leading scorer since joining five seasons ago, isn’t coming back anytime soon. Rozier, who ranks second on the team in shot attempts since being acquired from the Hornets in late January, is week-to-week with a neck injury.

Duncan Robinson, Miami’s best three-point shooter, is plagued by a back injury and played just a little over seven minutes without a shot attempt off the bench in Game 3.

Kevin Love, who has swung Miami’s net rating by minus-53.6 in 23 minutes of play, is a defensive liability in this series on pick-and-roll defense. He played only six minutes in Game 2 and saw action decrease to four minutes on Saturday.

One thing the Heat can definitely do, Adebayo said, is not allow the Celtics to get on the offensive glass and score as many second-chance points (17) as they did early on Saturday.

It was deflating.

“They were the more physical team,” Spoelstra said. “They bodied us, bullied us on screens, got through stuff, distorted screens, everything — flattened us out once we got past that first six, seven, eight minutes of the game. You have to credit them for that; they’re the more physical team, the team with more physicality and force on both ends of the court.”

Spoelstra isn’t folding, though.

He’s been short-handed before and led the eighth-seeded Heat to the NBA Finals a season ago.

“We have enough to get the job done. We understand the challenge,” Spoelstra said.

“We’ll get to work on getting a better version of ourselves for Monday night, which we’re fully capable of. We have competitors. Nobody feels good about this in our locker room, but we also respect Boston, what they’re capable of. We know how we have to be connected and have an incredible disposition with discipline and make the right play on both ends.”

Monday, we’ll find out if Spoelstra has another counterpunch for Mazzulla.

(Photo of the Heat bench: Jim Rassol /USA Today)