In Larry Bird's first prolonged absence since joining the NBA, the Boston Celtics have reached a low they hadn't hit since the season before he arrived.

The Dallas Mavericks beat Boston for only the second time ever Thursday night, 131-115, to give the Celtics their first losing month since April 1979, a string of 61 straight months. Bird, who is out for three months with bone spurs in his heels, joined the team in 1979-80. With only San Antonio to play before the new year, the Celtics have a 4-7 record in December.Dallas shot 62 percent in the first half and 57 percent for the game, climbing into a tie for the Midwest division lead with Houston.

Rolando Blackman scored 14 of his 32 points in the fourth quarter to hold off Boston. Most of the fourth quarter was played with Dallas star Mark Aguirre onthe bench.