The Thunder have upset the Spurs twice this season, I think there might be a key to what they do defensively. In the two games the Thunder have won, the Spurs shot about 24% from the three point line. The Spurs take jumpers 72% of the time, teams should clog the perimeter. Then, the Spurs can't get their role players involved and must penetrate or throw down to Tim Duncan.
Besides Tim Duncan, do the Spurs have a legitimate back to the basket scorer? I guess Drew Gooden can get you solid post offense, but other than that, they mostly have jump shooters. You also have guys who penetrate in like Parker and Ginobili. You need long, quick guys to defend them, but you know they're going to get their points eventually.
So, I'd approach it this way: never help off of the shooters, never double in the post (unless you have limited size) and make the Spurs big three score. If you can stop the Roger Mason's, the Bonner's, the Finley's for 3/4 of the game, they won't have much rhythm and could be ineffective if given chances to score. The Spurs three headed monster may be great, but if you take away the role players, the big three can't win a majority of games by themselves.
In a best of seven playoff series, a driving, big three offensive powered Spurs team is the team that is the most beatable. Take notes, lower level Western conference teams!
How would you defend the Spurs?