A balanced offensive performance and steely defensive display from the reigning NBA champions was enough to seal victory over the depleted Lakers, who started brightly but trailed for the final three quarters.
Chet Holmgren led the Thunder with 24 points and 12 rebounds while reigning NBA Most Valuable Player Shai Gilgeous-Alexander and Ajay Mitchell added 18 points apiece.
"We were a little choppy, a little rusty, but offensively we just stuck with it," Gilgeous-Alexander said, saluting a Thunder defense that restricted the Lakers to their lowest score in a playoff game since 2021.
"We just try to make people play outside their comfort zone, as simple as that," Gilgeous-Alexander said of the Thunder defense. "Whatever guys like to do, we like to take away from them."
The commanding Thunder victory underscored the size of the task facing the fourth-seeded Lakers if they are to defy the odds and upset the champions in the best-of-seven series.
Oklahoma City completed a 4-0 regular-season sweep over the Lakers, winning each game by an average margin of 29.3 points.
Tuesday's series-opener at Oklahoma City's Paycom Center echoed the Thunder's regular-season dominance, with the champions pulling away down the stretch to score an emphatic win.
James, who had defied his 41 years to lead the Lakers to a surprise 4-2 upset of the Houston Rockets in the first round, led Los Angeles with 27 points in a losing effort.
Rui Hachimura added 18 points, with Marcus Smart bagging 12 and DeAndre Ayton 10.
The Lakers saw Jarred Vanderbilt leave the game after he fully dislocated his right pinky finger while attempting a block. His status for Game 2 is questionable.