Ray Allen helped the Boston Celtics get into overtime and finish off the Grizzlies 116-110 on Saturday night in front of the first sellout crowd at Fedex Forum this season.

Paul Pierce scored 28 points, Rajon Rondo added 17 assists and Shaquille O’Neal dunked his way to 18 points as the Celtics concluded a 3-1 road trip and improved to 3-0 in overtime this season.

Allen hit a 3-pointer from the left corner and jumper from the wing early in overtime and the Grizzlies were held scoreless for the first three minutes to allow the Celtics to pull away.

Allen didn’t have a field goal through 3 1/2 quarters before nailing two 3-pointers and a wing jumper that gave Boston a 99-95 lead with 55 seconds left.

Rudy Gay hit a wing jumper nine seconds later and a pull-up jumper over Pierce in the lane with 7.3 seconds left after forcing Rondo into taking an off-balance shot to beat the shot clock. Pierce couldn’t get a shot off over Gay to end regulation.

Zach Randolph had 21 points and 11 rebounds and Gay scored 22 as Memphis allowed Boston to shoot 57.7 percent.