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The LeBron James-Anthony Davis Lakers won their first 59 games in which they led after three quarters. If last season's championship team led after three quarters, the game was functionally over. Not once did they blow such a lead, and that remarkable reliability came primarily from their defensive excellence. 

No team allowed fewer points per 100 possessions in the fourth quarter (100.8) than the Lakers last season. They were fourth in clutch defense prior to the Orlando bubble, and then improved in clutch settings when the playoffs arrived. Beating the Lakers late in games was almost impossible because scoring on the Lakers late in games was almost impossible. 

On Monday, the Portland Trail Blazers snapped that 59-game winning streak with a third-quarter lead. After falling behind 85-84 through three quarters, they outscored the Lakers 31-22 in the fourth to walk out of Staples Center with a 115-107 victory that last year's roster would never have allowed. But last year's roster didn't include Montrezl Harrell

The Lakers took a calculated risk on Harrell. In paying him only the mid-level exception, they managed to secure a player who, in a vacuum, was far more valuable than they reasonably should have had access to. They took him away from the rival Clippers, and assuming they were confident that Marc Gasol was coming for the minimum, they knew that they had a more traditional center coming to balance out his deficiencies. Harrell largely played well in his first three games as a Laker. His scoring, offensive rebounding and energy are genuine assets.

But those assets are best applied against bench lineups that he can physically manhandle. Asking him to play in crunch time puts a target on his back. That was especially true on Monday, as Frank Vogel left him on the floor for more than 15 consecutive minutes of game time. By the time Portland realized how exploitable he was on defense, he was too tired to fight back. That, in essence, is what lost the Lakers this game. The Blazers hunted Harrell into extinction on pick-and-rolls. 

Ostensibly, the Lakers decided on an aggressive pick-and-roll coverage against Damian Lillard to prevent him from dribbling into easy 3-pointers. This sort of trapping only works if the big defender hounds the ball-handler immediately off the screen, bothering him enough to allow the rest of the defense to rotate into place and perhaps force that ball-handler into panicking. Instead, Harrell got caught napping, not showing hard enough on Lillard to slow him down or dropping far enough back to do anything about Enes Kanter. He was in the middle of the play, yet he didn't affect either end of it. 

Harrell is slightly more attentive the next time Portland runs pick-and-roll, but still doesn't come up nearly high enough on C.J. McCollum. He leaves enough airspace for McCollum to bounce the ball into Jusuf Nurkic's pocket. LeBron James rotates, but he just isn't big enough to contest Nurkic here. 

A few plays later, Portland just catches him napping. He doesn't blitz or drop. He freezes, and by the time he realizes that Nurkic's screen is going to take Kentavious Caldwell-Pope out of the play, it's too late for him to scramble back to McCollum. 

As things grew dire, the Lakers abandoned the blitzing scheme to simplify things for Harrell. That didn't work either. When he drops back on this play, his only resistance to Lillard's drive is a lazy swat that results in a foul. 

The next time down the floor, Portland delivers the dagger. Another Lillard-Nurkic pick-and-roll. Harrell plays drop coverage again, but doesn't notice Nurkic leak back toward the middle of the floor. Lillard sneaks him the ball for an easy drive and layup. 

By this point, Vogel has seen enough. He pulls Harrell out of the game and replaces him with Kyle Kuzma, but the damage is done. Portland leads by eight with under two minutes to play, and the vaunted fourth-quarter Lakers defense had allowed a staggering 134.8 points per 100 possessions in the final frame. Game over. Blazers win. 

And it was a preventable win on a number of levels. A healthy and engaged Anthony Davis might have better been able to cover for Harrell on his missteps. Had Harrell been given a rest at some point in that 16-minute stint, he might have better been able to take on the more active defensive role Vogel's game-plan requires. This ultimately was a coaching loss, though, because Vogel didn't put his player in the best possible position to succeed. He asked an offensively-oriented sixth man to defend one of the most dangerous plays in all of basketball, and he got burned for it. 

On some level, that was probably intentional. The Lakers are four games into a 72-game slog. They have 11 players vying for major minutes and it isn't yet clear which of them fit best together. Home-court advantage doesn't need to be a priority when your biggest rival shares your arena. Vogel's goal isn't to win every regular-season game, but to use them to prepare for the postseason. He wanted to see how Harrell would respond defensively in crunch time against a contender. His fourth-quarter minutes were an experiment. 

But it was a failed experiment. The Lakers have now seen firsthand what happens when they abandon their defensive identity late in a game. It's a mistake they no longer need to repeat. Harrell can play a valuable role on this team. He just can't play the specific role he was asked to on Monday. When it counts, Davis or Marc Gasol should be at center in order to maximize the defense that ultimately made the Lakers a champion. That is the ticket to preserving the sort of leads the Lakers hope they never blow again.