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They had the lead in the third quarter, a chance to head back to Indiana needing just one win to reach the NBA Finals, and seemed poised to put the Miami Heat in a whole lot of trouble.

And then, it all went awry for the Pacers.

LeBron James and Udonis Haslem saw to that.

The Pacers are heading home, and instead of preparing for a possible coronation, it's elimination that they'll now try to stave off. A third quarter for the ages by the four-time MVP turned the game, with James scoring 16 of his 30 points in the period and the Heat beat the Pacers 90-79 in Game 5 of the Eastern Conference finals on Thursday night.

The Heat lead the series 3-2 going into Game 6 at Indiana on Saturday, win-or-else time for the Pacers.

"We've got to bring our energy," Pacers forward David West said. "Got to protect home court."

Or else.

James added eight rebounds and six assists, and Haslem made his last eight shots on the way to a 16-point night. Mario Chalmers scored 12 and Dwyane Wade added 10 for the Heat, who ousted the Pacers in six games in a second-round matchup last season and will look to do the same this time around, albeit one round deeper.

Paul George had 27 points and 11 rebounds for the Pacers, who got 22 points from Roy Hibbert and 17 from West. The Pacers led by seven at one point, but had no answer for the Heat in the third and now have to win back-to-back games — against a team that hasn't lost consecutive games since early January.

"Our backs are up against the wall again," Pacers coach Frank Vogel said. "Theirs were, they came back and responded, took care of business on their home court like they were supposed to. And it's up to us now to come back and get Game 6, see what happens in a Game 7."

Indiana was up 46-40 early in the third, surely sensing a chance to grab total control of the series. Over the next 11 minutes, the Heat outscored the Pacers 30-10, with James either scoring or accounting for 25 Miami points. He shot 7 for 10 in the third quarter; the Pacers shot 3 for 14. He had four rebounds in the quarter; the Pacers, as a team, grabbed six. He had four assists in the quarter; the Pacers had one.

"That's LeBron showing his greatness and making it look easy," Heat coach Erik Spoelstra said. "What we talked about was doing whatever it takes and competing for each other without leaving anything out there. His engine in that third quarter was incredible. He was tireless, he was making plays on both ends of the court, rebounding, covering so much ground defensively and then making virtually every play for us offensively. It's really remarkable."

Haslem said Juwan Howard threw a few things in the locker room and had a few choice words for teammates at halftime — "a lot of bleeps and stuff like that," Haslem said — and that James echoed the same remarks just before the start of the third.

"We had 24 minutes to play for our livelihoods," Haslem said. "And that's how we played in the second half."

Haslem's first shot of the night was a complete brick, bouncing off the top of the backboard. He was perfect the rest of the way, including going 5 for 5 in the third.

For the second time in the series, Haslem — who has struggled with his shot for the better part of two years — finished 8 for 9.

"That burned us," Vogel said.

Haslem got past Hibbert easily and into the lane for a dunk that put Miami up 47-46, the first Heat lead since 4-2. The Pacers were back on top by a point with 6:58 left in the third when fighting words reappeared, on a play where George Hill was called for an offensive foul after getting caught pushing off on a drive. West angrily approached Chalmers after the play and both of those players, along with Haslem, got technicals when it was all said and done.

It clearly fired up Miami.

James and Haslem combined to score 18 of their team's 21 points in the final 6:04 of the third. Everything came on jump shots, including a 3-pointer from Chalmers, three jumpers averaging 20 feet from Haslem, and five more from James, including a 3-pointer with 16 seconds left in the quarter that put Miami up 70-56 and had him yelling at no one in particular as the arena roared.

"I don't really know," Vogel said, when asked if there's anything a team can do when James gets on a roll like the one he had in the third. "He was pretty special tonight. There's no question about it. This whole team is special. It's one of the best teams that this league's ever seen and we're enjoying competing against them. We know we can beat them, but we've got to play better than we did tonight."

The NBA announced Thursday morning that it fined James, West and Lance Stephenson $5,000 each for flopping in Game 4, plus upgraded a foul that West committed against Wade in the fourth quarter of that game to a flagrant-1. Then Hibbert and West, speaking after Indiana's morning practice, said they have to protect their knees when Shane Battier is in the game for Miami, though neither flatly accused the Heat forward of dirty play.

And all that happened more than eight hours prior to game time.

Things didn't exactly calm down once the ball went into the air.

Indiana was blown out in Game 5 of a tied-up series at Miami last season, never holding the lead and losing by 32 points. This one took a much different tone from the outset, with the Pacers running out to a 15-9 lead that could have been worse for Miami given that West and Hibbert combined to miss three easy layups in the opening minutes.

"There's no question, we blew some opportunities in the first quarter," Vogel said.

George and Hibbert combined for all of Indiana's 23 points in the first quarter. Indiana's lead was four after the period, and when the second began, the reminders that these teams simply do not like each other started coming fast and furious.

Chris Andersen and Tyler Hansbrough needed to be separated early in the second, and both got technicals after Andersen appeared to hit Hansbrough twice, first with a shoulder and then with a two-hand shove. Andersen also picked up a flagrant-1 for his efforts, things cooled off a bit for the rest of the half, and Indiana went into the break up 44-40.

Then came the third, when Miami took control. A year ago, the Heat lost Game 5 of the East finals to Boston, and needed a 45-point game from James in Game 6 just to extend their season.

Not this time.

The finals are now one win away.

"That's what I came here for, to be able to compete for a championship each and every year," James said. "I'm one step away from doing it once again. It's not promised. It's not promised at all. I made a tough decision. Obviously, I think we all know the story. I envisioned something that was bigger as far as a team ... and we've got an opportunity as a team, once again, for the third year straight to make a trip to the NBA Finals."

NOTES: The last time Haslem had a 10-point third quarter was also against Indiana — but in March 2009. ... David Beckham was courtside near the Heat bench, Floyd Mayweather Jr. was courtside near the Pacers' bench. ... Hansbrough left in the fourth quarter with a sprained right ankle after falling over Battier, who was down on the court after going for a rebound.