When Daniel Murphy grounded to shortstop with the Washington Nationals trailing the Mets by two runs in the ninth inning Thursday night, Jayson Werth had a clear job to do: prevent the double play.

After Asdrubal Cabrera dived to his right to take a possible hit away from Murphy, he flipped to second to force Werth. Neil Walker’s throw to first pulled Kelly Johnson off the bag, but a slide interference call gave the Mets a double play, and the decision was upheld after the Nationals challenged the call.

In the wake of rules changes stemming from Chase Utley’s brutal takeout of Ruben Tejada in last year’s NLDS, Werth appeared to slide relatively late, knocked Walker down and did not maintain contact with the bag. Mets manager Terry Collins said the call was appropriate. “That’s how the rule is written,” he said. “There was contact above the knee, he was past the bag. All the things you can’t do. They got it right.”

Then Bryce Harper struck out swinging, sealing a 9-7 win for the Mets at Citi Field. But confusion and discontent over the call and the slide rule lingered well after the final out.

“To me, that’s a clean slide. It’s been a clean slide for over 100 years,” Werth said. “It’s a big spot in the game there . . . It seems like everybody’s got a different take on it. It seems like it’s inconsistent, whether it’s the rule or how many times it’s been changed.”

Werth added that there were three slides at second that went past the bag and said he asked an umpire for clarification on why they were deemed legal as they happened.

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“He said you’ve got to attempt to hold the bag,” Werth said. “I thought that brought some clarity to the rule. It turns out it went against me there in the ninth. Right now, I think it’s up to interpretation and I feel like it changes from day to day, from series to series and, in this case, inning to inning.”

Nationals manager Dusty Baker said he’s been told four or five different things by different crews and added that he hopes the confusion will be cleared up soon.

“I wish we’d get one answer on what we’re going to do with this double-play thing because it’s going to rear its ugly head in the playoffs or the World Series or something,” Baker said. “You’d hate to have a call like that decide whether you go to the World Series or whether you win the World Series. I think the crews are as confused as we are. I just hope — heck, man, we’ve got to get this straight because that’s terrible.”

With David Lennon