WASHINGTON — Noah Syndergaard threw a bullpen session Friday and proclaimed himself fit to start for the Mets on Sunday.

After the Mets’ 7-5 victory over the Nationals, Syndergaard said he thought he shouldn’t have been scratched from Thursday’s game because of right biceps tendinitis and said he “refused” to take an MRI on Thursday. Matt Harvey replaced him with only a few hours’ notice and was cuffed around in a loss to the Braves.

“I had a little hiccup in my arm,” Syndergaard said. “Threw a bullpen today and felt great. I was expecting to feel exactly how I did [Thursday]. But ready to go on Sunday now.”

Manager Terry Collins said the club was just being cautious with Syndergaard’s valuable right arm.

“I think so,” Syndergaard said. “But to me, I think I know my body best . . . I’m pretty in tune with my body and that’s exactly why I refused to take the MRI.’

Collins said Syndergaard had been feeling the arm discomfort for days, but the Mets did not give Harvey a heads-up that he was a candidate to start Thursday’s 1 p.m. game until that morning.

Harvey said after the game that he “wasn’t really physically prepared for starting” because he expected to pitch last night and had a hard workout Wednesday. Said Collins: “It’s news to me.”

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Cespedes to DL

The Mets placed Yoenis Cespedes on the 10-day disabled list with a strained left hamstring and called up lefthander Sean Gilmartin. Collins said an MRI on Cespedes “really didn’t [show] a lot, so it’s probably better news than we thought. It’s still going to be a while, obviously.” . . . Lucas Duda (hyperextended left elbow) went 1-for-3 in his first rehab game for Class A St. Lucie.