SAN FRANCISCO -- It's reached this point for the defending champions: They're not just on the brink of watching their season end prematurely. They're facing the prospect of being inflicted with the same frustrating, helpless end they've grown accustomed to delivering to everyone else.

There is irony in the way the Warriors, if they do not turn things around starting Thursday night in Game 5 of their Western Conference finals series against the Oklahoma City Thunder, are being undone.

They find themselves defenseless against Kevin Durant and Russell Westbrook despite a vaunted defense. The Warriors, exhausted and overwhelmed by a one-two superstar combo that is supposed to be their own strength, all but throw up their hands when the Thunder depth strikes next. And so they're left hoping those two great players simply ...miss shots.

Not much of a strategy. And exactly what Steph Curry and Klay Thompson did to the league throughout a regular season where they racked up 73 wins while making grown men -- the best athletes on earth -- feel helpless.

Turnabout is fair play, even if it doesn't feel like it.

"The series isn't over," Curry said after Game 4, with his team facing a 3-1 series hole. "We've got to believe in ourselves. It's obviously frustrating. It's a terrible feeling once again not stepping up and being ourselves and playing our game. But I think we're a special team and this isn't how we're going to go out."

That's all well and good -- and maybe, just maybe, he's right. But it's also worth underlining the words "frustration," "terrible feeling," and "not ... being ourselves." The Warriors made teams feel that way all season long. Now the Thunder are doing just that to them.

All series, Durant and Westbrook have looked like the unanimous MVPs of this league, like the combo that can't be stopped, like the offensive stars with a sterling defense that borders on the all-time great -- like, in short, the Warriors of the regular season.

It was the Warriors, in the regular season, that imposed their defensive will on opponents, good for 100.9 points per 100 possessions -- fifth best in the league. They were even better last season.

While that has evaporated this series, the Thunder have suddenly become a team capable of making the most exciting offense in years looks downright pedestrian. Oklahoma City has a 101.8 defensive rating, markedly better than what they did in the regular season. It's as if they stole Golden State's defense and, as part of the trick, gave them their own lackluster defense and stagnant offense in return.

Part of that is Russell Westbrook's athletic prowess on that side of the ball. But it's also true that the Thunder have mastered Warriors basketball: Play fast, drop buckets, and still shock them with defense. This is the fastest pace of play in a Conference or NBA Finals since 1990, a fact that should play to the Warriors great advantage. They had the fastest pace of play this season, while the Thunder were 10th in that category. But, again, it's the Thunder mastering the Warriors by mastering what they did to win all year long against them.

That pace of play in the regular season was part of the reason Curry led the league with 30.1 points per game. Durant was third with 28.2 pointer per game, and Westbrook eighth at 23.5. But in this series, Westbrook and Curry have basically switched spots in scoring. It's Durant leading the way in the conference finals (28.5 points per game), then Westbrook (27.3), with Curry a distant third (24.3).

There's also, past the numbers and scoring and defense, a swagger and belief that filled Oracle and opposing arenas this season as the Warriors unleashed their excellence. I covered a lot of these games, and their belief and confidence and how it manifested itself in real wins and greatness was unparalleled.

That hasn't just evaporated against Durant, Westbrook & Co. It's been wholly coopted. It's now the Thunder that prowl around with an air of invincibility.

The Spurs had only lost one home game all season long? The Thunder take two there.

The Warriors lost only twice at home this season. The Thunder pranced into Oracle and won there, too, in Game 1.

It's bad enough to lose, to let go of a dream of greatness and a belief that you and your teammates have no equals on a basketball court. But the Thunder are doing more: They're doing to the Warriors just what the Warriors did to everyone else all season long.

Curry's right: It's a terrible feeling indeed.