Russell Westbrook scored 23 points and Kevin Durant added 22 of his own to lift the Thunder over Toronto 104-92 on Sunday, handing the Raptors their second straight loss after they had won eight of nine.
"I praised our guys, the way we played, fought, scrapped," Casey said. "But at the end of the day, reality set in."
Alan Anderson had a career-high 27 points — 19 of them in the second quarter — for Toronto (12-22). Amir Johnson finished with 19 points and nine rebounds and Jose Calderon had 10 points to go with 11 assists.
The Thunder held DeMar DeRozan — Toronto's leading scorer this season — to 11 points.
"We wanted to make sure we didn't give (DeRozan) any easy shots," Thunder coach Scott Brooks said. "He's an athletic guy that can get to the rim and his mid-range game is good."
Serge Ibaka added 19 points for the Thunder (26-7), while Kevin Martin had 16.
The Raptors were coming off a lacklustre 105-96 loss to the Sacramento Kings two nights earlier that had ended their five-game winning streak at home.
While the players were pleased with their effort Sunday, the Thunder showed why they're one of the best teams in the NBA.
"We compete, we fight, we did a lot of good things," Calderon said. "But against this team we cannot make one turnover, you make a mistake you're going to pay for that. I think every little mistake we made tonight it turned into a basket or a foul or something.
"It's about a good team, and every mistake they're going to make you pay. These kinds of teams, you've got to play perfect for 48 (minutes)."
The Raptors held their own over the first half thanks to a sizzling second quarter that saw Anderson drain four three-pointers and Kyle Lowry add a pair. Lowry, who finished with 10 points and eight assists, made like he was tucking a three-fingered gun in his holster after hitting a long-range basket.
But after trailing the Thunder by just two points at halftime, Oklahoma City had put 15 points on the home team by late in the third quarter and took a 78-67 lead into the final 12 minutes.
Toronto pulled to within nine early in the fourth but couldn't make up any more ground in front of a crowd of 18,203 fans at the Air Canada Centre. A three-pointer by Lowry with three and half minutes to go had the Raptors within 13, but Westbrook drained a three on the Thunder's next possession, Kendrick Perkins scored on an emphatic dunk and it was game over for Toronto in the third contest of a six-game homestand.
"It's tough especially when you're playing a playoff-contending team," Johnson said. "You can't make any errors. You have to man up and play one-on-one defence, you have to stop the turnovers and take care of the ball."
The Raptors gave up 23 points on 17 turnovers.
Casey called the game a chance for his players to test themselves against the best.
"They've done probably one of the best jobs in the league in building a program and developing players from scratch. They're king of the hill now," Casey said. "You can go right down the line, everybody knows their role, they know their position, they know who they are."
The Raptors played their 10th straight game without forward Andrea Bargnani, sixth without rookie forward Jonas Valanciunas, and third minus Linas Kleiza — creating what Casey called "a chemistry lab" of different lineups.
On top of that, Raptors rookie Terrence Ross left the game a minute into the fourth quarter with a sprained left ankle.
Ibaka scored 10 points in the opening quarter, with his dunk giving the Thunder an 11-point lead just seven minutes into the game. The Thunder led 23-18 to end the first.
Toronto went on a 21-8 run early in the second, capped by a three-pointer by Lowry that gave the Raptors a five-point lead. It was short-lived, however, and Oklahoma City had a 52-50 advantage at halftime.
Notes: Raptors forward Aaron Gray (stomach bug) didn't dress. ... Former Raptors guard Muggsy Bogues was at the game. ... The Raptors host Philadelphia on Wednesday, Charlotte on Friday and will cap their homestand next Sunday against Milwaukee.