The Houston Rockets upstaged defending NBA champions the Cleveland Cavaliers, while the Boston Rockets beat the slumping Chicago Bulls.
James Harden posted a triple-double as the Rockets triumphed 117-112 at home to LeBron James and the Cavaliers on Sunday.
The Bulls were handed a fifth successive loss, beaten 100-80 by the Celtics.
Damian Lillard inspired the Portland Trail Blazers against the Phoenix Suns.
HARDEN OUTDUELS LEBRON IN MVP BATTLE
It was a battle of the MVP contenders and Harden came out on top against James.
Harden posted 38 points, 11 assists and 10 rebounds, compared to 30 points from James.
It was Harden's 16th triple-double of the season and his 31st game with at least 30 points as the Cavs crashed to a fourth defeat in five outings.
CELTICS HEAP FURTHER PAIN ON BULLS
The Celtics put the sorry Bulls to the sword thanks to 22 points from Isaiah Thomas.
Star Bulls pair Dwyane Wade and Jimmy Butler were limited to eight and five points respectively on the road.
LILLARD LEADS TRAIL BLAZERS, PACERS BEAT HEAT
Lillard had 28 of his 39 points in the first half as the Portland Trail Blazers defeated the Phoenix Suns 110-101 and the Indiana Pacers accounted for the Miami Heat 102-98.
The Philadelphia 76ers were too good for the Los Angeles Lakers 118-116, while the Brooklyn Nets downed the New York Knicks 120-112.
CAN BULLS END SLUMP?
The Bulls are facing a sixth consecutive defeat as they prepare to take on the Charlotte Hornets on Monday. The San Antonio Spurs host the Atlanta Hawks, the Los Angeles Clippers are at the Utah Jazz, while the Toronto Raptors welcome the Dallas Mavericks.