OKLAHOMA CITY — The Celtics played a strong first half, but nothing came easy afterwards against the hottest team in the NBA. The C’s were dominated in the second half as they lost 105-92 to the Thunder on Sunday at Paycom Center. The C’s dropped to 26-10 while the Thunder improved to 30-5 with their 15th straight victory.

Both teams knew the assignment Sunday — right from tipoff, the intensity and environment lived up to the billing. The shot-making was on point as it was an entertaining game between the reigning champs and the West’s best team.

While it was a back-and-forth first quarter, the Celtics created some distance as part of a strong second quarter to take a 10-point halftime lead. The C’s were the better team early as they leaned on their double big lineup for a physicality advantage.

But the C’s offense sputtered against the league’s best defense. The Celtics mustered just 15 points in the third quarter, going 1-for-13 on 3s. The Thunder weren’t lighting the world on fire either, but their stout defense allowed them back into the game. Then they ran away with the victory in the fourth quarter, outscoring the Celtics 29-12 in the frame.

Jayson Tatum had 26 points and 10 rebounds for the Celtics while Jaylen Brown added another 21 points. MVP candidate Shai Gilgeous-Alexander finished with 33 points and 11 rebounds for the Thunder.

The Celtics finish their four-game road trip by taking on the Nuggets at 10 p.m. Tuesday in Denver. Here are four takeaways from Boston’s loss to Oklahoma City:

Second half collapse: The Celtics were an efficient machine through the first half against the league’s best defense. But they were on their heels in the second half. The Celtics were just 3-for-24 on 3-pointers in the second half as their jumpers abandoned them. Not only did that allow the Thunder back into the game, but the Celtics didn’t have an answer from there against the Oklahoma City defense. All in all, the Thunder outscored the Celtics 50-27 in the second half. It was a complete different showing than the first half for both squads. While the C’s had a solid process early, that wasn’t the case in the final two quarters.

Matchup of magnitude: There was no need to hype up Sunday’s game. It was a showdown between the West’s best against the reigning NBA champs. Of course, fans were going to bill it as a potential NBA Finals matchup. Both teams played like a playoff game as loose balls needed to be earned amid a mad scramble of bodies. And it was the Thunder, looking to make their own mark on the league, who came out with the victory Sunday.

Finally healthy: Sunday was the first time the Celtics were at full strength with their top-8 rotation players available since Nov. 29 in a win over the Bulls. That was 17 games ago. Even then, that was just Kristaps Porzingis’ second game since returning from surgery rehab, so he wasn’t at full strength. So, the Celtics showed the good parts in the first half. But their second-half struggles were also part of the equation.

Road trip continues: The Celtics will have to pick up themselves after Sunday’s tough loss. They’re now 2-1 on this tough four-game road trip with the 2023 NBA champs coming up on the road. The Thunder have been one of the best teams in the league thus far this season, so a loss isn’t necessarily alarming. Though that second half was a tough showing for the C’s.