The Oklahoma City Thunder beat the Memphis Grizzlies 131-80 in Game 1 of their first-round Western Conference playoff series on Sunday, the fifth-biggest margin of victory in NBA postseason history.

The 51-point margin was seven points shy of the record and was the largest Game 1 win in NBA playoff history.

Aaron Wiggins scored 21 points, Jalen Williams scored 20 points and Chet Holmgren had 19 points and 10 rebounds. Shai Gilgeous-Alexander, the league’s scoring champion with nearly 33 points per game, scored just 15. The host Thunder still shot 50.5% from the field.

“We played to our identity,” Gilgeous-Alexander said. “Nothing more, nothing less than that. We were who we were all year ... and it’s going to be the key to our success, just staying true to who we are.”

Gilgeous-Alexander had said several times since Oklahoma City’s loss to Dallas in last season’s Western Conference semifinals that he would be intentional about getting his teammates better prepared for this postseason.

So far, so good.

“I have a great group of guys around me, and I know that,” Gilgeous-Alexander said. “And I’ve known that for a long time. ... They obviously played amazing.”

There have been two 58-point playoff margins in NBA history: Denver beating New Orleans 121-63 in 2009 and the Minneapolis Lakers beating the St. Louis Hawks 133-75 in 1956. The Los Angeles Lakers beat Golden State by 56 (126-70) in 1973 and the Chicago Bulls beat the Milwaukee Bucks by 54 (120-66) in 2015.

Ja Morant scored 17 points for Memphis on just 6-for-17 shooting. Jaren Jackson Jr., who averaged just more than 22 points in the regular season, scored four points on 2-for-13 shooting. The Grizzlies shot just 34.4% overall.

Game 2 is Tuesday.

Eastern Conference

Derrick White scored 30 points, Jayson Tatum had 17 points and finished the game after a scary late fall, and the Celtics beat the Orlando Magic 103-86 in Game 1 of their first-round playoff series in Boston.

Payton Pritchard added 19 points off the bench for Boston, which hosts Game 2 on Wednesday. Jaylen Brown played 31 minutes and had 16 points on 6-of-14 shooting after missing the final three games of the regular season due to a lingering knee issue.

With Boston leading 89-73 with 8:28 remaining, Tatum went up for a dunk and was hit hard by Kentavious Caldwell-Pope as he tried to block it. Tatum landed awkwardly on his right side.

He stayed down briefly before eventually rising to his feet, clenching his right hand. After a video review by referees, Caldwell-Pope’s foul was upgraded to a flagrant foul.

Paolo Banchero led the Magic with 36 points and 11 rebounds. Franz Wagner added 23 points for Orlando, which has not made it out of the first round of the playoffs since the 2009-10 season.

Cavaliers 121, Heat 100 >> Donovan Mitchell scored 30 points and Ty Jerome had 16 of his 28 points in the fourth quarter for host Cleveland in Game 1 of the first-round playoff series.

It was the seventh straight series in which Mitchell has scored at least 30 points in Game 1, tying Michael Jordan, who had two streaks of seven games.

Bam Adebayo had 24 points and Tyler Herro added 21 for the Heat. They are the first No. 10 seed to advance to the playoffs out of the Play-In Tournament.

Darius Garland added 27 for the Cavaliers, who host Game 2 on Wednesday night.