Australia's Josh Giddey has led Oklahoma City's scoring with 20 points and added 11 assists but couldn't prevent Memphis winning a clash of youthful NBA teams.
Morant and John Konchar added 19 points each for Memphis, with Morant finishing with 11 assists and Konchar grabbing 10 rebounds.
Jalen Williams had 16 points, six rebounds and seven assists for the Thunder but star Shai Gilgeous-Alexander had his lowest scoring game of the season with 15 points, going six of 18 from the field.
Twenty-year-old Giddey is averaging 14.5 points a game in his second NBA season, up two points from his rookie year.
Grizzlies coach Taylor Jenkins said Morant had "tweaked" his ankle.
The Grizzlies (9-6) are sixth in the western conference while the Thunder (7-8) are 11th.
In Salt Lake City, Lauri Markkanen scored a career-high 38 points, including an improbable turnaround jumper to beat the shot clock with 38.5 seconds left as hosts Utah Jazz beat the Phoenix Suns 134-133.
After scoring 45 points through three quarters, Suns star Devin Booker had just two free throws in the final quarter and an inconsequential bank shot at the buzzer to finish with 49.
Chris Paul missed his fifth game with a right heel injury and the Suns have gone 2-3 without him.
In New Orleans, the Boston Celtics recorded a ninth straight win as they beat the Pelicans 117-109.
Giannis Antetokounmpo led the Bucks with 25 points and 14 rebounds, however, his struggles from the free-throw line - he went 4 of 15 - were amplified with each attempt in the second half by a raucous Philadelphia crowd.
In San Francisco, defending champions Golden State improved to 7-1 at home with a 111-101 win over the New York Knicks but have an 0-8 road start.
In Washington, Bradley Beal scored 27 points, Kristaps Porzingis had 20 points and a season-high 17 rebounds and Washington beat undermanned Miami 107-106 in overtime.
In Cleveland, Darius Garland scored 41 points, Donovan Mitchell added 34 and the Cleveland Cavaliers survived a fourth-quarter collapse to beat the Charlotte Hornets 132-122 in double overtime and snap a five-game losing streak.