LeBron James, left, had a huge first half for the Cavaliers last night, pouring in 23 points. Defending for the Celtics are Paul Pierce (34) and Kendrick Perkins.

The Providence Journal / Glenn Osmundson

BOSTON — At some point in this playoff series, you just knew that LeBron James was going to throw the fear of God into the Boston Celtics. Last night was that night.

By halftime in the always-critical Game Five at TD Banknorth Garden, the Boston Celtics appeared to be in a heap of trouble. James had awoken from his series-long shooting slumber and helped the Cavs to leads of as many as 14 points by pouring home 23 points in 20 eye-opening minutes.

Even so, the Celtics didn’t panic. In fact, they barely noticed. Coach Doc Rivers said he hardly brought up James at intermission. He simply stressed patience, control and the urgency to play with poise.

“We hadn’t played well and LeBron had played great and it was, what, a two-point game?” said Rivers.

Actually, it was 46-43, Cleveland. A 14-3 finish to the half wiped out much of the Cavalier’s lead and when the Celtics took control in a dominant third quarter, they left James in their wake and ran away for a 96-89 victory. Boston can close out the Cavs with another win in Game Six tomorrow night back in Ohio.

Regardless of Rivers’ calmness, this one boiled down to stopping James. After scoring every which way in the first half, he was limited to 12 in the second while missing seven of his 11 shots. James finished with a game-high 35 points but the only other Cavs to score in double figures were Delonte West (21) and Wally Szczerbiak (10).

The Celtics’ best players played big with Kevin Garnett going off for 26 points and 16 rebounds and Paul Pierce pouring home 29, including the final eight under pressure from the free-throw line. But the Celtic James called the “X Factor” was point guard Rajon Rondo. He used his quickness to all but live in the lane and went on to score 20 points and dish off for 13 assists.

“We know we’ve got our work cut out for us as we go out on the road and try to close this out, which is the most important thing right now,” said Pierce. “It’s a good win for us to take the lead here but we have to close it out, which is the toughest part.”

While disappointed, the Cavs weren’t crushed. Szczerbiak admitted the Cavs have run out of room in this series, but he says they’ll own plenty of confidence in a return to Quicken Loans Arena tomorrow.

James was more emphatic. “We know it’s win or go home, but a LeBron James team is never desperate,” he said.

The Celtics played like the desperate team in the second half last night. After James cruised around Pierce, James Posey and everyone else in a fantastic (8-for-14 shooting) first half, the Celtics regrouped. Actually, their late second-quarter rush, which included two unlikely 3-pointers from Rondo, really started the team’s engines.

“In the second quarter we had a lot more energy,” said Garnett. “Rondo hit some big shots for us, guys were in the flow, then we carried it over into the third quarter.”

Rivers didn’t change anything defensively on James except to push his defense to become more aggressive.

“He was beating his guy before the double-team could come. In the second half, we did a better job forcing him to double teams,” Rivers said. “He’s a great player. He’s going to have great games and we still have to find a way to win the game and our guys did that tonight.”

The start of the third quarter was an offensive feast for the Celtics. They quickly wiped out Cleveland’s lead with the help of two Cavs turnovers and the Celts pulled ahead after making nine of their first 11 shots to grab a 62-57 lead. Garnett scored eight points during the run, three on jump shots. The Celts kept rolling and capped a 12-for-16 (75 percent) shooting quarter with two Garnett assists, one to Glen Davis for a layup and another to Piece for a big-time jam. James scored his only field goal of the quarter on a running floater in traffic with 44 ticks left but the Celts ended the quarter up by nine points, 72-63.

They opened the fourth with Davis scoring again in the lane. When Allen found Davis for a third layup two minutes later, the Celts had taken full control, 76-66. Boston led, 88-77, with three minutes left but didn’t close the game well. The Cavs scored five points in a row to make it 88-82 and Pierce kept the door open with a missed layup. Szczerbiak then had a wide-open look at a 3-pointer, but missed. Pierce hit two free throws to make to 91-84 and kept the Cavs at bay with five more free throws down the stretch to ice the game.

kmcnamar@projo.com