BOSTON - The Boston Celtics are in the playoffs. The Detroit Pistons aren’t far behind.

Boston became the first NBA team to clinch a postseason berth, getting a season-high 31 points from Kevin Garnett on Wednesday night to earn a bruising 90-78 victory over Detroit, its closest competitor in the Eastern Conference.

“That’s not what we want,” Boston coach Doc Rivers said. “That’s nice, but last year it would have been a parade.”

The Celtics missed the playoffs the last two seasons, but the arrival of Garnett and Ray Allen has raised expectations for the NBA’s most-decorated franchise. So even though Wednesday’s victory ended their playoff drought, it was more important because it gave them a 2-1 victory in the season series with Detroit.

“It was good to beat them in the regular season and win the series, but this is a team we’re probably going to see in the playoffs,” said Paul Pierce, who scored 15 points. “They’ll be a better team by then.”

But if the Pistons (44-17) tie the Celtics (47-12) in the standings and meet them in the playoffs, Boston would have the home-court advantage. That could be crucial, considering the way the teams banged into each other the first three times they played this season.

“Any time you play another elite team it will be a playoff atmosphere. All three felt like that,” said Chauncey Billups, who scored 23 points, going 14-of-15 from the line. “It was very physical. That’s what we like to do. That’s great basketball and all games should be like that.”

The idea gave Rivers pause.

“I don’t want to think about that,” he said. “But the way I look at it is if we do see them again, it’s only a good thing.”

Kendrick Perkins had a career-high 20 rebounds to go with his 10 points, and Rajon Rondo had 16 points to help Boston win its sixth consecutive game.

“All these games count,” said Garnett, who scored five straight points after the Pistons tied it 69-69 in the fourth quarter. “We are trying to get home-court advantage. ...All these games are huge for us.”

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Rasheed Wallace also scored 23 for Detroit, Richard Hamilton scored 15 and Tayshaun Prince had 10 rebounds, seven points and five assists.

The Pistons never led, falling behind 17-3 off the opening tip and working their way back to a 69-69 tie on Tayshaun Prince’s putback for the first basket of the fourth quarter. But Garnett made a free throw, a jumper and a layup and, after Detroit cut it to 78-77, the Celtics scored 12 of the last 13 points.

It was an anticlimactic ending to a hard-fought game, with three technical fouls handed out along with hard fouls that sent players to the floor. Allen drew the first technical with a clearing elbow to Hamilton’s chest in the first quarter; in the third, Jason Maxiell clobbered Rondo to the parquet after a breakaway dunk.

Tony Allen’s layup gave Boston a 78-74 lead with 6:01 left in the game, but he was called for a technical foul — apparently for celebrating — that cut a point off the lead and Hamilton calmly sank a 23-footer from the top of the key to make it a one-point game.

But Pierce hit a 3 to make it 81-77. Rondo drew a charging foul on Billups, and the Pistons guard was called for a technical that gave the Celtics an 82-77 lead.

After a Pistons miss, Rondo got the loose ball and threw it upcourt, where Pierce grabbed it and put it in for an 85-77 lead.

It was over.

The Celtics took a 23-13 lead after the first quarter, shooting 59 percent to 26 percent for the Pistons. But Wallace scored 14 in second quarter — Garnett had 12 — and the Pistons scored eight straight points to make it 25-23.

Juan Dixon had a chance to give Detroit the lead, but he missed a 3-pointer. The Celtics scored 11 consecutive points — 10 in a row from Garnett — to make it 38-25.

The Pistons finally pulled even early in the fourth after Billups and Prince scored the last seven points of the third, then Prince tied it with 10:50 left in the game.

Notes: The Pistons won 87-85 in the first meeting this season. Boston won 92-85 in the second. ...Billups made all 11 of his free throws and scored 18 in the third quarter. ...Garnett needs 23 points to reach 20,000 in his career.