Boston guard Marcus Smart drives to the basket as Miami’s Max Strus defends during Game 5 of theEastern Conference finals Thursday night at TD Garden in Boston. Charles Krupa/Associated Press

BOSTON — If Marcus Smart plays like he did in Game 5 the rest of the series, the Celtics will pull off a miracle.

That’s right. With all due respect to Jimmy Butler, just pencil it into the record books.

If that Smart shows up from here on out, playing lights out on both ends of the floor, the Celtics will become the first NBA team to erase a three-love hole, and beat the Heat in seven games.

Count on it.

That’s what Good Marcus means to the Celtics. He’s the one – not Jayson Tatum or Jaylen Brown – who most naturally breathes life into this team. He’s the player everyone feeds off, especially if he plays as well as he did in do-or-die Game 5.

Five seconds in, Smart immediately set the tone with a defensive gem, stripping the ball from Miami’s Bam Adebayo, diving on the loose ball, then getting it to Tatum for a layup and a quick lead.

The Celtics never trailed from that point on, coasting past the Heat 110-97, and sending the series back to Miami down three games to two.

Perhaps Coach Joe Mazzulla put it best in assessing Smart’s overall performance and importance on the team: “He’s just an emotional key for us. When he’s locked in and playing both sides of the ball at a different pace, it kind of gives us our identity and our life.”

He was a lifeline all right.

That opening play was the first of five steals for Smart, a career-high for him during the postseason. Let’s just say when the Celtics are at their best, they take on Smart’s personality which is one predicated on fearlessness, hustle and determination.

As Mazzulla said, that became the Celtics’ identity Thursday night.

That initial theft by Smart, created by his relentlessness and effort, immediately established the Celtics defensive mindset and intensity, pushing the pace and generating points in transition.

Smart not only sparked the defensive effort, he added 23 points, hitting 4 of 6 from 3-point land. It was Smart and White (six 3s en route to a game-high 24) who led the charge, and pushed the series to a sixth game. Tatum and Brown, meanwhile, finished with 21 points apiece.

Seriously, the Celtics can’t lose if that’s what they get out of Smart every night.

While Bad Marcus shows up and tends to force things offensively, taking ill-advised 3-pointers over Tatum and Brown, thinking he’s as important to the offense as they are, he struck just the right balance in Game 5.

While Tatum and Brown provide the one-two superstar punch, Smart is often the straw that stirs the drink. If he stays in that lane, the Celtics are virtually unbeatable.

Smart was certainly the catalyst in the first quarter. He triggered an offensive outburst that saw the team go on a 14-0 run after taking a 6-5 lead. He was a constant pain in the Heat’s behind all game. Smart just provides that missing intangible to get the team going. At least, that’s what stood out to Tatum during this win.

“Smart diving on the floor, getting out in transition, that was contagious,” Tatum said. “Smart just played his ass off tonight.”

Facing an impossible deficit, Smart knows it’s on him to lead the way, and have the team feed off of his energy. As great as Tatum and Brown are, they don’t lead in the same way Smart does. And while the veteran guard was aided by Gabe Vincent’s absence with a left ankle injury, that shouldn’t diminish the job he did Thursday night.

“I wanted to get us going,” Smart said following the win. “I just wanted to come in and give my team some energy early.”

Smart was aggressive from jump, and didn’t let the Heat get comfortable with any of their possessions. And keeping Butler (14 points) and his supporting cast uncomfortable has been a huge reason why the Celtics have been able to extend the series.

The best way for the Celtics stay off the roller coaster that’s been plaguing them through the playoffs, at least in terms of energy and effort, is for Smart to just clone that performance going forward.

When Mazzulla took him out with 6:08 remaining, with the Celtics enjoying a huge lead, Smart not only received a rousing ovation from the crowd, but from the players on the bench.

To a man, all of his teammates were quick to point out just important his performance was in Game 5.

“Smart was just a beast tonight,” said Brown. “I don’t know what game y’all guys was watching, but Marcus on both sides of the ball was incredible tonight. It was a great performance from him. ”

They just need more of the same. They need more of Good Marcus.

Because if that guy keeps showing up, it’s on to Denver.