BOSTON — No preseason? No problem for Rajon Rondo.

“He absolutely destroyed us Friday in practice,” Boston Celtics coach Brad Stevens said after his point guard returned after missing the exhibition slate with a broken hand and led the Celtics to a 121-105 rout of the Brooklyn Nets in the opener for both teams Wednesday night.

“I thought (Friday) was really great until I watched the film and then I thought our team stunk, as far as in that practice. So that was a little bit of fool’s gold, I thought. But the last couple of days … he looks like himself, what I’d seen on film before I got here.

“I don’t think he ever looked like that any time last year because he was coming back.”

Last year was Rondo’s first season back from knee surgery. On Wednesday night, after he said he decided to play following his afternoon nap, he scored 13 points, dished out 11 assists and grabbed seven rebounds in 29:45 to lead eight Celtics in double figures against the lead-footed Nets.

“He is back to full speed,” Stevens said. “He had a couple of turnovers yesterday in practice when we were going up and down but he was flying. It’s good to see. It’s really good to see.”

Playing with a pad protecting his left hand, Rondo, hurt in a household fall, turned the ball over on Boston’s first possession but then notched his first assist 1:37 into the game. He went on to record four more assists in the quarter as his team took a nine-point lead after one.

He scored only two points in the first half but then scored nine in a 1:06 span of the third quarter.

Rondo, who was 6-of-9 from the floor, including a banked 3-pointer, and 0-for-4 from the foul line, banged his knee in the fourth quarter but didn’t leave the game.

“I felt pretty fast tonight … I think I was around 91 percent,” Rondo said. “It was just fun being back out there. I missed the game.”

Center Kelly Olynyk scored 19 points, forward Jeff Green had 17, guard Avery Bradley 15, forward Jared Sullinger 13 and swingman Evan Turner, energy rookie guard Marcus Smart and guard Marcus Thornton 10 apiece for Boston.

“It just made everyone feel a lot more comfortable,” Bradley said of having Rondo back. “He’s our leader and he came out and played amazing; like he didn’t miss a beat, almost like he hadn’t been off at all.”

The Celtics, who led by 26 points at the half, kept pushing the pace and built a 29-point lead through three quarters. The Nets, playing their first game under new coach Lionel Hollins, made a mild run at the start of the fourth quarter but were never really in this game.

“They had 62 points in the paint and most of them were non-contested,” said Hollins.

Forward Mirza Teletovic went 4-of-6 from 3-point range and led Brooklyn with 20 points, while guards Deron Williams and Joe Johnson scored 19 apiece. Williams added eight assists, but the two scorers took 35 shots, making 13.

Former Celtics big man Kevin Garnett, starting his 20th season, was greeted with a huge pregame ovation and scored 10 points and grabbed six rebounds. He also had a disagreement with Olynyk after the center set a hard screen on Brooklyn swingman Alan Anderson. Garnett received a technical foul.

“It’s not the game we wanted, but obviously we have room for improvement,” said Garnett. “We did some great things, but not enough to win. Hat goes off to the Celtics. They played great tonight.

“Rondo was classy. I don’t know, he was at 89 or 93 percent. He played well and led his team to a win tonight.”

NOTES: Oft-injured Nets C Brook Lopez is out again, with a right foot sprain, and C Mason Plumlee is got the start. “He’s still having some pain when he goes hard,” said coach Lionel Hollins, who made his Nets coaching debut in the opener. … Patriots QB Tom Brady took to Facebook to wish the Celtics well, complete with a picture of a teenage Brady wearing a photo-shopped Celtics headband. … Former Celtics F-C Kevin Garnett got a rousing ovation when introduced before the game, as did G Rajon Rondo, who addressed the crowd before tipoff. … Isaiah Austin, the young center from Baylor whose career was ended before it started, was honored by the Celtics. He was presented with a framed Celtics jersey (No. 21) and made an honorary Celtic for life.