The Spurs won their last 10 games of the regular season and their first 10 games of the playoffs before running out of steam against an Oklahoma City team facing a must-win situation.
San Antonio's lead in the Western Conference finals was cut to 2-1 and the Thunder will try to even the series when they host Game 4 Saturday.
Oklahoma City outscored the Spurs by 15 in the second quarter to take a 54-41 halftime lead, and then pulled away over the final two periods.
Spurs Coach Gregg Popovich, who consistently rested his veteran stars during the lockout-shortened regular campaign, kept his starters on the bench as the Thunder began to turn the game into a rout. No San Antonio starter played more than 28 minutes.
Oklahoma City shot 45 percent from the field and missed only one of its 17 free throws.
Durant, the NBA's leading scorer during the regular season, hit 8-of-17 from the field. Thabo Sefolosha added 19 points and clamped down defensively on San Antonio's Tony Parker. Sefolosha also contributed six rebounds and made six steals.
James Harden added 15 points for the Thunder and Serge Ibaka chipped in 14. Russell Westbrook was only 5-of-15 from the field for 10 points, but he had seven rebounds and nine assists while committing just one foul.
Oklahoma City limited the Spurs to 39 percent shooting and forced 21 turnovers.