LAS VEGAS -- It was a rough outing Sunday for the Portland Trail Blazers summer league squad and their two rookies, Zach Collins and Caleb Swanigan.

Portland shot only 29 percent from the field and lost 70-64 to the Boston Celtics.

Collins, the 10th overall pick in June's NBA draft, was impressive on defense with six rebounds, three steals and two blocked shots. But he struggled on offense for the second game in a row, scoring only five points. He missed six of his seven shot attempts and went 3 for 6 from the free-throw line.

Swanigan, who earned positive reviews with a double-double in his summer-league debut Saturday, didn't play as well Sunday against the Celtics. He scored 12 points, missing eight of his 12 field goal attempts. He added 7 rebounds, two assists and a steal.

Photos: Blazers in summer league play

Portland's two other roster players, Pat Connaughton and Jake Layman, didn't fare well either. Layman shot 1 for 13 from the field, missing all five of his 3-point attempts, and finished with seven points. Connaughton scored a couple of late buckets to finish with 11 points. He led the team with four assists but also had four turnovers.

Boston rookie Jayson Tatum had 11 points and seven rebounds and second-year player Jaylen Brown had 13 points and eight rebounds.

The Blazers play their third summer-league game Tuesday against the San Antonio Spurs. That game tips off at 1 p.m. and will be broadcast on NBA-TV.