Harden made four 3-pointers early to help Houston build a 34-22 lead in the first quarter. Oklahoma City scored seven straight points after that, before Harden added a pair of free throws to lead the Rockets up 36-29 at the end of the first quarter.
"I hadn't made four 3s all season in one game," Harden said. "I took some extra shots last night, that kind of helped me out with my confidence a little bit, just to get it going early — not trying to force it, but get my teammates involved and everything else was going to open up."
Parsons was helped off the court and into the locker room after twisting his right ankle near the end of the third quarter.
He returned with about 6 1/2 minutes left in the game.
NOTES: The Rockets reached agreements on two trades that will send Patrick Patterson, Cole Aldrich and Toney Douglas to Sacramento and Marcus Morris to Phoenix, a person familiar with the situation said Wednesday. The Rockets will receive Thomas Robinson, the No. 5 pick in last year's draft, Francisco Garcia and Tyler Honeycutt from the Kings, according to the person, who spoke on condition of anonymity because the deal had not been announced and was still pending league approval. ... Thunder center Kendrick Perkins missed Wednesday's game with a sprained right knee. ... Wednesday was Houston's ninth double-digit comeback win this season.
AP Sports Writer Chris Duncan contributed to this report