The Celtics couldn’t run sets without the Blazers pushing the pace, swiping balls loose, racing up the floor, heaving shots, and rebounding many of the misses.

It wasn’t until the third quarter that the Celtics finally found a rhythm.

Ray Allen, who had been scorching this month but ice cold all night, hit a 3-pointer. Kendrick Perkins flushed a two-handed dunk. Allen drilled another 3-pointer, then weaved through the paint for a layup. Each bucket came off feeds from Kevin Garnett, and the Celtics took a 62-52 lead, up to that point their biggest of the night.

That lead was enough to cushion the Celtics’ win no matter how haywire things got.

Allen finished with 18 points, knocking down 3 of his 6 3-pointers. Perkins had 10 points and 9 rebounds in 21 minutes, stretching the playing time coach Doc Rivers had originally prescribed, with Perkins playing just his second game since returning from ACL surgery.

Paul Pierce scored 17 points, keeping the Celtics afloat while the Blazers ran a fire drill in the first half, frustrating the Celtics into countless turnovers. Pierce left the game in the closing minutes and went to the locker room.

The first of a four-game road trip wasn’t exactly pretty. Perkins would grab a rebound, turn, and sling it up court for Rajon Rondo, not seeing LaMarcus Aldridge stretching his 6-foot-11-inch frame to swat it down.

Allen would wait on the wing for a feed from Rondo, then he’d bobble it slightly but just enough for Rudy Fernandez to grab it, and dart the other way to start a fast break.

The Celtics finished with 21 turnovers, and somehow won in spite of them all.

For the Celtics, everything was out of place. For the Blazers, it was organized chaos.

The teams combined for 20 first-half turnovers. Every shot seemed to bounce of the rim, and every rebound seemed to spark a fight (in the red corner Joel Przybilla, in the blue corner Kendrick Perkins).

Between technical fouls (Pierce) and the tension from a packed Rose Garden, the pace and atmosphere were frantic.

The Blazers resisted every Celtics’ attempt to restore order.

When Patty Mills’s 3-point attempt swirled around the rim, the Celtics stared instead of grabbing it. Dante Cunningham flew into the picture and tapped it in off the glass to give the Blazers a 24-23 lead.

It was the first bucket in an 11-4 burst for the Blazers. LaMarcus Aldridge was taking most of the shots and gobbling up the rebounds (11 in the first half), but Mills and Cunningham were the second-quarter catalysts.

With Garnett and Allen running cold (a combined 4 of 14 in the first half), Pierce was left to respond.

Pierce scored 8 points in the second quarter, including a 3-pointer that put the Celtics up, 40-34, with 1:58 left.

Pierce drilled a 3-pointer that put the Celtics up, 44-37, as soon as he came out of the locker room for the second half, but the Celtics were in a rat race.

It seemed as if it would boil over, and it nearly did early in the third quarter, when Przybilla set a hard screen that sent Rondo to the floor.

Perkins, playing just his second game after recovering from ACL surgery last July, settled into his enforcer’s duties, getting nose-to-nose with Przybilla while Rondo was laying on the floor.

The two big men had to be separated by Garnett.

Rivers’s biggest worry entering the game was controlling the tempo and even though the game was low scoring, the pace was troubling from the outset.

When Mills sent the ball on a zipline to Aldridge for an alley-oop — his second of the quarter — the Blazers cut the Celtics’ lead to 21-18 and Rivers called a timeout.

But the Blazers kept scrapping.

They missed 16 of 25 first-quarter shots. Aldridge was the only player with more than one basket. The rest of the team was 5-of-17 shooting.

The Celtics’ six first-quarter turnovers were like life preserves for the Blazers, who turned them into 8 points. The Celtics also gave up six offensive rebounds, but the Blazers struggled to capitalize on the second chances.