BOSTON – When Rajon Rondo entered training camp, the Celtics wanted him to show that he could be a consistent star night in and night out.

That didn’t mean scoring 20 points a night. It meant running the offense efficiently, taking advantage of his scoring opportunities when they arose, and playing tenacious defense.

The Celtics knew that he was talented, and Doc Rivers said he was the best point guard to run the team, but the Celtics wanted to make sure that Rondo would be a positive force for the team both on the court and in the community before giving into his demands of a five-year, $55-million contract.

Through training camp and the opening month of the season, Rondo was a model citizen. He ignored the distractions of not having a contract through the first four games, when he quarterbacked the Celtics to a 4-0 record by handing out 11.8 assists per game to go along with his 6.5 points and 5 rebounds.

After that, and by what he had done in his previous three years, the Celtics decided to lock up their point guard of the future by giving him the money he wanted.

Rondo no longer feels like he has something to prove, and he did not appear complacent after signing his big contract. He averaged 12.6 points, 7.2 assists, 3.4 steals and 2.6 rebounds over his next five games before having two subpar performances in which he recorded a combined 14 points and 13 assists in losses to Atlanta and Indiana.

The Celtics don’t believe it is a coincidence that they lost and Rondo struggled. Captain Paul Pierce said the offense and defense begins with Rondo, and when Rondo is playing well, the Celtics are tough to beat.

So after Rondo struggled in the first half against Golden State on Wednesday night, Pierce pulled Rondo aside in the locker room and motivated him to play better.

What Pierce told Rondo, Kevin Garnett said, was personal, but whatever he said, it worked. Rondo came out and scored 12 points, grabbed four rebounds, and handed out three assists in the third quarter alone. He finished with 18 points, 12 assists and 7 rebounds.

The Celtics outscored the Warriors, 31-19, in the momentum-shifting third quarter to break open a close game.

Both Pierce and Garnett said that Rondo was the difference.

“I thought he changed the momentum of the game,” Garnett said on Wednesday night. “I thought he was a lot more solid. He was aggressive. He picked up the energy.”

“He was terrific in the second half,” Rivers said of Rondo. “He came out in the third quarter and played with unbelievable speed and energy.”

“That might be the only player in the league who can average a triple-double for a season,” Warriors center and former teammate Mikki Moore said.

“We started calling plays for me on the pick-and-roll and I just tried to attack the bigs,” Rondo said.

Rondo’s second-half performance is what the Celtics are hoping to see out of him every night over the next five years.

“He’s got to play on his instincts, and his speed always had to be the deciding factor,” Rivers said. “He’s one of the rare players in our league that can play at great speed and stay under control and see everything. Most players can’t do that, and he can.

“We told them before the game they’re going to switch a lot. And if Rondo came off with enough speed, it didn’t matter if they switched. They couldn’t stay in front of him. And he did that in the second half. He was terrific.

“When he plays like that, we’re really good.”

Rondo still needs to work on his free-throw shooting. He has made just 4 of 16 free throws (25 percent) so far this season and at one point, had a streak of 11 straight misses. But that doesn’t mean he is going to stop attacking the basket and getting fouled.

“It’s not life or death. It’s a miss or make,” Rondo said of his free-throw struggles. “I don’t put too much into it and I’m gonna keep attacking the rim. I think I’m averaging like eight layups a game. I’m not shying away from the rim. I’m going to keep attacking and I’m going to keep going to the line.”

roblee@projo.com