Wilmer Flores erupted for four hits and three RBI out of the cleanup spot for the Mets on Saturday, but it wasn’t enough to propel the team to victory.

Starter Robert Gsellman fell apart at the seams early on, surrendering six runs (two earned) on nine hits while walking two and striking out one to put the Mets in an early hole, and Jeurys Familia was rusty in his first action in three months, tagged for three runs in the ninth.

“Again, he’s still a young guy. Last year when he came up, there was a whole different circumstances,” Mets manager Terry Collins said about Gsellman. “He was in good shape and had been pitching good and just kept going.”

After Gsellman retired Howie Kendrick to begin his day, a fielding gaff by the pitcher allowed Wilmer Difo to reach first.

Anthony Rendon doubled to put runners in scoring position with just one out, but it wouldn’t require a splendid offensive play to put across the first run as Difo scored on a wild pitch.

First baseman Adam Lind then put up another run with a fielder’s choice and the Nats doubled their score two batters later on a two-run single off the bat of Adrian Sanchez.

In the second, Lind struck again, driving in the Nats fifth run of the game with a sharp single to right.

The Mets got on the board in the second after a double from Jose Reyes with two outs, who would score on a single from Juan Lagares.

Rendon tacked on another run for Washington in the fourth, which would send Gsellman to the showers.

The righty labored through four innings and was demoted to Triple-A after the outing.

“It’s very frustrating,” Gsellman said after being informed he was demoted. “Nobody likes losing. It’s been tough, but you got to keep your head up.”

Chasen Bradford and Josh Smoker combined to toss three scoreless innings in relief of Gsellman, striking out four while not surrendering a hit.

In the sixth, the Mets attempted to chip away at the deficit as Flores, known this weekend as “Catire,” launched his 16th long ball of the campaign off Nationals starter Gio Gonzalez.

Flores plated two more in the eight inning, trimming the Nats lead to 6-4 with a double to right that was upheld by a challenge.

However, in the ninth, Jeurys Familia took the mound for the first time since May 10, but didn’t fare well as the fireballer surrendered three runs in one inning of work.

“I think maybe two more outings I’ll be ok,” said Familia. “I have to get used to it, then I will be fine. My arm feels great. 100 percent, that’s all that matters right now.”

Kevin Plawecki went 2-for-3 out of the sixth hole for the Mets, while Travis Taijeron wore the collar, going 0-for-4 in his major league debut. Amed Rosario also made an outstanding grab in the third inning to rob Andrew Stevenson of a hit.

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