Payton Pritchard scored 26 points hours after agreeing to a four-year, $30 million contract extension, and the Boston Celtics beat the Philadelphia 76ers 114-106 on Sunday in the preseason opener for both teams. Pritchard shot 9 for 14, including 6 for 11 on 3-pointers, and had four assists in 23 minutes for the Celtics. Pritchard’s three-point play gave Boston a 102-101 lead with 4:28 left to play and the Celtics stayed in front from there.