by Ryan ZumMallen / @ryanzummallen

During Game 4 of the Western Conference Finals, while Dirk Nowitzki was busy turning his defender into Collisonwurst and Thunder head coach Scott Brooks was busy not calling plays, it became painfully aware that Oklahoma City is dead in the water unless its most important player balls to his potential.

No, not Kevin Durant. Russell Westbrook? Think again. Without question, the most important player on the Oklahoma City Thunder is the 21-year old sixth man with the “Old Man’s Game.”

After a lukewarm rookie season, no one could have predicted that second-year forward James Harden would be as indispensable as he has been to the Thunder in these playoffs. While the basketball world has obsessed itself with hashtags about his facial hair and phantom flop, Harden has worked his way into a niche that the Thunder now cannot function without. And when he committed an indefensible, mindless sixth foul on an opposite-end rebound with Oklahoma City four minutes away from tieing the series, it became clear how indispensable Harden is to this team.

Dirk and ze Mavsensteinns rattled off a 15-2 run, then steamrolled the Thunder in overtime for a demoralizing win and a 3-1 series lead. Oklahoma City committed silly turnovers, ruined final shot opportunities and didn’t even realize they had possession until there were six seconds left on the shot clock, but it wasn’t about what they did so much as what they were missing.

On the bench was a player who has emerged as a star as much as Russell Westbrook has emerged as a tease. Don’t agree that Harden is more valuable? Westbrook sits entire fourth quarter in Game 2? Thunder win. Harden sits with 4:33 remaining and a 13-point lead in Game 4? Thunder lose.

You tell me.

This is not to say that Harden is Oklahoma City’s best player. You’d have to be high off sizzurp to say it’s anyone but Durant. But without Harden, Durant and Westbrook were unable to exploit their natural offensive advantages, and Dallas easily handled OKC’s dribble-dribble-shoot strategy. Maverick defenders forced Durant to catch just outside of Arkansas, and trapped the ball out of Westbrook’s hands. Without the extra ball handling, penetration and jump shooting that Harden brings to the floor – and since Brooks patently refused to draw anything resembling an offensive set – the Thunder were left to rely on overdribbling and Serge Ibaka jumpers. And we saw how that worked out.

Harden doesn’t put up LeBronian stats – or even Pippenesque stats – but that Old Man’s Game that has become a common punchline is exactly what allows the Westbrook freestyle and Durant lethality to shine. All he has to do is be on the damn floor. He’s like the Jason Bateman of the Oklahoma City Thunder.

Harden played just 23 minutes in Game 4, his lowest playing time in these playoffs. In that tick, the Thunder were +4 with him on the floor. If Harden doesn’t foul out and the Thunder go +4 over the next four minutes, they win by 17 points instead of losing by 7.

So tonight, no one is quite sure how the Thunder are going to come out for Game 5. Do they come out swinging, a la Grizzlies? Or perhaps put up a Laker-inspired meltdown? If Durant & Co. plan to avoid looking like a bunch of Bynums out there, they would be wise to make Harden a focal point of the offense. Going back to early April, the Thunder are 6-0 when the bearded one scores 15 points, and just 5-8 when he doesn’t.

Durant is going to score, Westbrook to going to slice and Dirk is going to Dirk (yes, this is now a verb). The playoffs are about controlling what you can control. And if the Thunder are going to stay alive, they can control the fluency of their offense – something that was nonexistent late in Game 4 – by keeping Harden on the floor as much as possible. There’s no trick or offensive wrinkle to this strategy. It just works when he’s on the floor, and it usually leads to a Thunder win.

There’s a name for that. Old Man’s Game.

Ryan is a SLAM contributor and a second cousin (by marriage, but still) to Dr. James Naismith. You can follow him on Twitter at @ryanzummallen