The Celtics  showed no mercy on the weary Detroit Pistons  on Thursday night at TD Banknorth Garden , demolishing them, 98-80. The first quarter was a wake-up call as the Green fell behind 13-2 in the first three and a half minutes. But for the final three quarters, this one belonged entirely to the defending champs. Rajon Rondo  looked better than he has all season, scoring 18 and controlling Allen Iverson  and the tempo all night. This was the second time this season the 11-2 Celtics have owned Detroit, beating them 88-76 back on Nov. 9. There are 69 games remaining but it’s hard to imagine anyone in the East knocking the Celtics out of the top perch. Next up tonight, Kevin Garnett  gets to actually play in his return to Minnesota to take on the Timberwolves . Last year, he had to sit on the sidelines because of an injury.