Young Kevin Porter sparked a third-period explosion as the Capital Bullets came back to completely disorganize the Boston Celtics Sunday in rolling to a 112-99 victory.

Porter, getting a chance to play while veteran Archie Clark rested a sore elbow, scored 15 of his 23 points in the third period of the nationally-televised game at Boston Garden.

Trailing 52-48 at the half, the Bullets outscored the Celtics 36-20 in the third quarter and were in command the rest of the way. At one stage, Capital scored 13 straight points and outscored Boston 21-4 in just over five minutes of action.

Porter got plenty of help from backcourt mate Phil Chenier, who hit for 29 points, and big Elvin Hayes, who had 25. Mike Rierdon contributed 20, mostly with his long bombs.

The Celtics Jumped to a 25-19 first period lead on the shooting of Jo Jo White and John Havlicek. They managed to cling to the advantage, and widen the margin to nine points midway through the second period before the Bullets began their comeback.

Porter, a second-year player, stole the ball from Boston's Don Chaney and went in all alone to put the Bullets in front to stay 59-48, just 4:17 into the their period. Then the Bullets applied all-out pressure, foreign Boston to miss easy shots and also throw the ball away.

White topped the Boston scorers with 26 points while Havlicek finished with 23 and Dave Cowens with 17.