The Boston Celtics clinched a playoff spot on Wednesday with a 90-78 victory over the Detroit Pistons in a battle of the NBA’s two best teams.

Even though there is still more than a month remaining in the season, the Celtics (47-12) became the first club to secure a postseason berth with a win and losses by New Jersey, Atlanta and Indiana.

Boston now has a four-game lead over Detroit (44-17) in the battle for the NBA’s best record.

“This was a big game for us, man, you know to win this, we have the top record,” Celtics forward Kevin Garnett said. “It’s just a big game.”

“Last year, it would’ve been a parade,” Boston coach Doc Rivers said of clinching a postseason berth.

The Celtics, who have won six in a row, will likely add veteran guard Sam Cassell to the lineup on Friday vs. Chicago.

Cassell signed with Boston on Tuesday after being waived by the Los Angeles Clippers last week. He joins the Celtics’ “Big Three” of Garnett, Paul Pierce and Ray Allen.