Roberts dominated 7-foot center Steven Adams and just about every other Thunder player who tried to keep him from attacking the rim.
The 6-foot-8, 215-pounder made 5 of 6 shots while starting at center in place of Nerlens Noel.
The Sixers wanted Noel to take a day off to rest because he has been going hard since the start of summer-league training camp. The center missed last season while he recovered from knee surgery.
Noel and rookie swingman KJ McDaniels are scheduled to play in both the Orlando and Las Vegas summer leagues. Noel had game highs of 19 points and four steals in an 83-77 loss to the Magic on Saturday.
"He's scheduled to play again this week," said assistant coach Lloyd Pierce, who is coaching the Sixers in the Orlando league. "Nothing is off course with him. . . . We are going to get in the gym and do something very light tomorrow. I'm pretty sure he will be playing again either Tuesday or Wednesday, hopefully both. Whatever it is will be a team decision."
Roberts made the most of his time filling in.
"I just start off by saying I'm going to get every rebound," Roberts said. "Then after that, I just let everything else fall into place. I'm going to get the putback offensive rebound and I'm just going to get a dunk to get everything started."
Sixers point guard Casper Ware finished with a team-high 20 points.
The Sixers also sat Hollis Thompson, who has a sore left knee. Forward Melvin Ejim left the team because he did not get any playing time on Saturday.
Serbian point guard Vasilije Micic, whom the Sixers drafted 52d overall last week, will not participate in either of the summer leagues. The 6-5, 203-pounder will not play for the Sixers this season.
Micic will stay overseas and play for Mega Vizura of the Serbian League for at least one more season.