Rarely has so much been at stake in a Game 7 that precedes the NBA Finals.

But on a steamy Saturday night, two teams sensed the end of their grand alliances if they lost. Or a chance to get the one thing they united for if they won.

Do-or-die. Go to Oklahoma City or go fishing. Validation or elimination.

For the Miami Heat and LeBron James, the king without a crown, the entire season has been an all-or-nothing proposition. It came down to the closing minutes of the Eastern Conference finals against the stubborn Boston Celtics.

That’s when the Heat’s Big 3 collaborated just the way they had planned for two years. When it counted most they did not choke and they did not miss in a thrilling 101-88 victory.

As time drained from the fourth quarter, James slammed the gavel down on a right-handed dunk, then sank a three-pointer from Biscayne Boulevard. He fed Chris Bosh for a silky jump shot. Bosh blocked a Rajon Rondo attempt. Dwyane Wade flung the ball into the basket as he crashed to the floor and sank the accompanying free throw. With the Heat’s lead growing, Bosh grabbed a rebound and Wade rescued a loose ball.

Just like that, everything clicked the way it had been foreseen for the Big 3 in the finale of this exhausting, entertaining series. James, Wade and Bosh scored all 28 of Miami’s points in the fourth quarter.

With the game, their future and their coach’s job in the balance, they buried the Celtics with a 20-6 avalanche in the final eight minutes. They were breathtaking; the Celtics were breathless.

Thus, the Heat was spared the wake many had predicted for them. The Celtics had to answer questions about their last gasp, their demise and the breakup of the banged-up 30-something Big Three of Kevin Garnett, Paul Pierce and Ray Allen and their point guard wizard Rondo, who had another triple-double.

The Heat advances to the NBA Finals for the second straight year to pursue the title it’s been expected to win since The Decision by James and his smiling prediction of multiple championships two summers ago. The euphoria that filled AmericanAirlines Arena will quickly turn to nervous anticipation. The Heat was supposed to arrive at this point, and go well beyond it.

“We got a lot more work to do,” Wade said during the trophy ceremony.

James came to Miami in large part to remove the Boston barrier from his path to the title, to “get over the hump,” as he put it, against his familiar foe.

He followed his surreal 45-point, 15-rebound masterpiece in Game 6 with 31 points, 12 rebounds, two assists and a block in Game 7. When Miami was on the brink, down 3-2, he came through in Boston when it counted most. When Miami looked vulnerable with eight minutes to go, James again took control.

The Heat overcame two opponents in this Game 7 test: The resilient Celtics and relentless scrutiny from judgmental critics and skeptics who want James and the Heat to fail.

Will it be enough? No. He’s got to do it all over again starting Tuesday against the loaded Oklahoma City Thunder. The affable, sunny-faced Kevin Durant will be the perfect foil for those who view James as a caricature of villainy for his abandonment of Cleveland.

He’s got to ignore the naysayers with the same stoicism he’s shown in the past two games.

“I’m happy for this brotherhood,” Heat coach Erik Spoelstra said. “We’ve been through a lot and it’s developed character and we’ll need it in the next round.