OKLAHOMA CITY — Keldon Johnson finally got his offensive game going in the Western Conference finals with a series-best 15 points in Game 5, but it was hard for the NBA’s Sixth Man of the Year to feel good about it after the Spurs fell 127-114 to the Oklahoma City Thunder.

“It really doesn’t mean anything if we don’t win,” he said. “The most important thing is winning, and we didn’t do that tonight, so everything else goes out the window.”

Something else that went out the window Tuesday night: The smothering defensive effort the Spurs produced in pounding the Thunder 103-82 in Game 4 in San Antonio.

Everything the Spurs did right on that end of the court Sunday seemed to vanish Tuesday night. 

“It just felt like it was a little bit of everything in terms of we did not put ourselves in position enough to be successful in each possession,” Spurs coach Mitch Johnson said when asked what went wrong defensively.

Asked specifically about the Spurs losing the second quarter 40-31 to go into halftime down 69-58, Johnson complained of players being in the “wrong positions or wrong coverages” or making “poor decisions.”

Spurs forward Devin Vassell offered a more succinct explanation for what went wrong defensively.

“Undisciplined. Undisciplined rotations. Undisciplined fouls. That’s about it,” said Vassell, who scored just six points on 2 of 11 from the field and 2 of 9 beyond the arc in his first single-digit performance of the playoffs.

Keldon Johnson agreed about the “undisciplined” assessment.

“We just committed too many fouls, too many fouls away from the basket, things like that,” he said. “We got into the bonus early. When they get to the foul line, it slows down the pace.”

De’Aaron Fox, who scored just nine points on 4 of 15 from the field and 0 of 4 from distance, said the Spurs allowed the Thunder to become “too comfortable” offensively.

“When that happens, they start making threes, start touching the paint,” he said. “We had bad fouls, put them on the line too many times, things of that nature. We just have to tighten up on that end.”

Julian Champagnie, who finished with a playoff-high 22 points, said it all might have boiled down to effort.

“They were the more desperate team tonight,” he said. “I thought they wanted the game more than we did.”