Oklahoma City took control of the series in Games 3 and 4 with their ability to protect the rim and ignite the fast break. Serge Ibaka returned to the line-up and had the luxury of defending a non-shooter and a non-scorer in Splitter, so he could camp out in the lane and clog up the Spurs offense. Keeping either Bonner or Boris Diaw on the floor forced Ibaka out of the paint and out of his comfort zone.
With Ibaka at the 4 and Kendrick Perkins/Steven Adams at the 5, the Thunder guards could press out on defense and jump the passing lanes. However, with only one big in the paint, the Spurs had more breathing room on offense and more driving lanes to the rim. On the pick-and-roll, OKC's second line of defense was a wing instead of a shot-blocker. The game became a lot easier for San Antonio.
You could see the effects up and down the Spurs rotation. Splitter is far more effective backup center than Aron Baynes, so the move made their second unit better on offense and defense. Splitter is a really good individual defender at the 4, but there isn't a LaMarcus Aldridge or Dirk Nowitzki in this series. The same would hold true in a hypothetical matchup with the Heat in the NBA Finals.
There's no great adjustment for Brooks to make in Game 6. You could try to attack Bonner on defense, but neither Ibaka nor Perkins is a natural shot-creator. Where they could have a big advantage is pounding the offensive glass. They also have to hope that Diaw doesn't bring his three-point shot to OKC. If they can shrink the floor on Diaw, like they did in Games 3 and 4, it negates a lot of the Spurs spacing.
They lost control of the game in the second quarter, when Brooks had Caron Butler and Derek Fisher on the wings next to Reggie Jackson. That line-up just doesn't work because they are making Jackson do everything when Kevin Durant and Russell Westbrook are out. Butler and Fisher are very limited players on both sides of the ball - they can't really move their feet and they aren't driving threats.
What's so maddening about that is Jeremy Lamb clearly outplayed both guys in Games 3 and 4 and he still couldn't get minutes over them. These are the kind of coaching moves that drive people bananas when they watch Brooks. Playing Butler over Lamb is questionable but playing Fisher over him is absolutely inexcusable. At a certain point, as a coach, you have to respect the game.
Fisher got in the and promptly turned it over twice and had Ginobili and Patty Mills reign 3's on his head. I wrote this about after Game 3 - I'm not sure you can afford to have a guy like Fisher in the rotation and beat a team as good as San Antonio. The guy is shooting 28% from the field in the playoffs. I'm really not sure what more Brooks has to see. It would be funny if it weren't so sad.
He also needs to take a page out of Erik Spoelstra's book - Miami staggers their rotation so that at least one of Wade or LeBron is in the entire game. Westbrook and Durant are both capable of carrying an offense for stretches, so there's no reason to have big chunks of the game with both in and chunks when they are both out. These are the small rotation adjustments that Brooks is always behind on.
I still think OKC is in decent shape - they should play much better defense at home in Game 6 and the Spurs shooters aren't likely to be as locked in. However, they are still going to have to steal a game on the road and staggering Splitter and Duncan made the Spurs a much tougher match-up. The margin for error is very thin and the Thunder can't afford for Brooks to ignore the numbers and play his friends.