Eric Gay/Associated Press

Game 1 and Game 2 of the NBA Finals played out largely the same: A back-and-forth affair with Miami slightly in the lead the whole way. In Game 1, cramping forced LeBron James out of the game and handed San Antonio the victory. In Game 2, he played down the stretch and squeezed out the win for the Heat.

As per usual, his offense was outstanding. There were moments of his selfish brilliance, bulldozing his way to the rim for easy layups and dunks. In the second half, he lit it up from the perimeter, draining three-pointers and step-back jumpers. As the game came to a close, it was his crucial pass to Chris Bosh for a corner three that put Miami ahead for good.

But the fourth quarter wasn't about LeBron's offense so much as it was about his defense. Because he's one of the best defenders in the league, it's tempting for Heat head coach Erik Spoelstra to stick LeBron on Tony Parker or Manu Ginobili the entire game. The problem is that Spoelstra needs to save his legs on offense, so he usually gives him an easier assignment for the first three quarters.

The fourth quarter is when LeBron's true defensive dominance is unleashed, with Spoelstra assigning him Parker—a decision that completely unhinges the San Antonio offense.

Parker is a successful NBA point guard for multiple reasons, but it's primarily his dribble penetration that allows him to thrive. He's essentially quicker than every player in the NBA, and his drives almost always draw secondary defenders. If the help doesn't come, he scores. If it does, he kicks the ball out to an open shooter, leading to San Antonio's beautiful ball movement that unravels any scrambling defense.

For the first three quarters of games against Miami, Parker usually faces off against Mario Chalmers or Norris Cole. Both are solid defenders in their own right, but neither are quick enough to handle Parker. In the fourth, it's LeBron's turn. Though Parker still has the quickness advantage, LeBron's combination of size, length and recovery speed shifts Miami's coverages against Parker penetration.

James will typically lay off of Parker on the perimeter, giving him room to shoot. Because Parker is not a particularly great jump shooter from three-point range, he usually passes up these shots.

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Instead, he tries to penetrate and sometimes can gain a slight advantage against James.

The difference is that James' superior athleticism allows him to block almost all of Parker's shots from behind. The space James gives up initially also gives him time to slide his feet and physically overmatch Parker. What's normally a small crease Parker can slide through closes up as he simply bounces back off of James.

Only once in the final six minutes of Game 2 did Parker even attempt to attack James, and it didn't go well.

But what's key isn't James' defense on Parker; it's no surprise that James won the matchup. This play is about how the rest of the Miami defense reacts—or, to be more precise, doesn't react.

Miami trusts that LeBron can handle Parker in any one-on-one scenario. Even if Parker does gain a step, James' length and speed give him adequate time to recover and block the shot. The more dangerous aspect of Parker's game is his ball distribution, and Miami rightfully worries about shooters lighting it up from deep.

The trust in James to defend Parker allows his teammates to stay at home on shooters, giving Parker no other option than to recklessly attack James. Notice what happens here as he goes at LeBron: None of the Miami defenders move significantly, giving Parker zero release valve.

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Parker is literally driving right next to Dwayne Wade, yet Wade doesn't even turn his back to help. He's sticking to Ginobili, no matter what. Same goes for Mario Chalmers: Kawhi Leonard is a dangerous corner three-point shooter, and Chalmers only briefly stunts at Parker before quickly scurrying back to Leonard.

On the weak side, Chris Bosh is only one arm's length away from Duncan even as Parker enters the paint. He's wary of the dump-off pass.

It's therefore completely on Parker to create something, which he's unable to do. He eventually dribbles himself into the short corner, gets stuck and nearly turns it over when James easily strips him.

As Matthew Tynan of 48 Minutes of Hell notes, these type of isolation plays don't work against Miami: "The offense broke down into uncharacteristic isolations, and when you play that game against James, Dwyane Wade and Chris Bosh, you’ll almost always lose."

Ray Allen saw it the same way, according to Barry Jackson of the Miami Herald: "The Heat's fourth quarter defense, Ray Allen said, 'was the difference.'"

Give San Antonio credit for recognizing the mismatch and opting for other offensive avenues. For most of the final six minutes, the offense was initiated through Ginobili or Duncan, with Parker heading to the corner as a floor spacer.

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Because he's not a great shooter, James could cheat off him toward the middle to protect the paint.

On this play, San Antonio isn't able to generate anything out of a Ginobili-Duncan pick-and-roll, and Ginobili settles for a three-pointer three feet behind the arc. Parker, meanwhile, is camping out in the corner completely uninvolved in the possession.

One minor adjustment completely rejiggered San Antonio's offense, nullifying the wonderful offensive ability of Parker: blanketing him with LeBron. While Ginobili and Duncan are great players in their own right, they're better playing off Parker. Parker is the true penetrator, the true point guard. He's the one that makes the Spurs' offensive machine purr, and without him, San Antonio struggled.

It's this type of play that proves LeBron James' dominance as a defender. Obviously he can't sustain that level of intensity on both ends of the floor for the entire game, so it's no shock that his defensive legs are usually saved for the fourth quarter. But when it's finally his time to shine on defense, Parker doesn't stand a chance.

Moving forward, we can expect this matchup late in the fourth quarter of every game. In Game 1, the Spurs got lucky with LeBron's cramping injury. In Game 2, LeBron was at full strength and in full defensive lockdown mode on Parker down the stretch. Until the Spurs figure out how to get the neutralized Parker going, they'll have a lot of trouble closing out games.