WASHINGTON - Jonathon Niese retreated to the dugout, where he waved his arms and muttered as he slammed his glove into the bench.

Just a few days earlier, Terry Collins had called Monday's start against the Nationals the biggest of Niese's career. It proved to be a dud.

"We're going to get this thing right," said Niese, who was shelled for five runs in 31/3 innings in the Mets' 8-5 victory.

Niese's anger stemmed from the curveball he threw to Wilson Ramos, which came to rest above the Mets' bullpen. The grand slam shaped Niese's five-run implosion in the fourth.

"I promise you guys I'm not insane because I've been making the same mistake the last three games trying to get different results," Niese said. "It's just not working."

The outing, he said, unraveled after one bad pitch.

Said Collins: "That's what he was upset most about."

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With Matt Harvey's innings cap creating doubt about his availability, the Mets need Niese, who has a 10.53 ERA in his last four starts.

What's next?

Yoenis Cespedes downplayed questions about his looming free agency.

"I don't really know what [the Mets are] thinking," said Cespedes, who was 3-for-5 with a homer and a pair of doubles. "But my plan is to go out there and have fun. I enjoy the team. This is a really great team. I love the city of New York. I love the fans, and what we've got going here is a really good thing."

Extra bases

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