Harden, playing against the team that traded him away just before the season started, posted 20 points, but the league's second-highest scoring offense was held 15 points below its regular-season average while shooting 36 percent.
"We were trying to be solid on the defensive end," Durant said. "We knew they were a great scoring team. We just tried to pack the paint and get out to their shooters. We had to make the second and third efforts, and I think we did that."
The Thunder were already up by 23 when Larry Hill connected on the half-court shot and went bounding toward Oklahoma City's huddle in celebration, getting congratulated by Thabo Sefolosha before the team's bison mascot pulled him back away.
Durant's dunk sparked a string of seven straight points for Oklahoma City, and Harden never even came off the bench in the fourth quarter. Coach Scott Brooks called a timeout and pulled Durant a few moments later, and reserves finished out the game for the Thunder.
Westbrook ended up with 19 points, 10 assists and 8 rebounds. Serge Ibaka chipped in 17 points and Kevin Martin, Harden's replacement in the sixth man role, had nine of his 16 points in the fourth quarter with the game already in hand.
It was an impressive playoff opener for top-seeded Oklahoma City, which made it to the NBA Finals last season before losing to Miami in five games.
"We wanted to take care of our home court," Durant said. "We didn't do anything yet."