Bartolo Colon was just 27, a chiseled, bright-eyed, flame-throwing marvel with his whole career still ahead of him. This was long before the years and the pounds and the metamorphosis into baseball’s keg-shaped, strike-throwing metronome.

Until the Mets’ unsightly 7-1 loss to the Nationals Wednesday night, it had been nearly 16 years since Colon walked five batters, plunked another, and lasted less than five innings in a start.

Bryce Harper, the feared Nationals slugger, was still a 7-year-old looking forward to Funyuns and Slurpees after taking grounders and batting practice with his dad.

Yet here was Colon, the veteran righthander looking out of sorts as he allowed three runs and five hits in 4 2⁄3 innings. He walked five and hit a batter.

His bout of once-in-a-decade wildness came on the same day that a report surfaced that the married father of four is being sued by another woman, who is seeking child support for their two children.

“When I’m here doing my job, nothing else affects me, thank God,” Colon said through a translator, insisting that his off-field issues had little to do with his performance.

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His only support came when Yoenis Cespedes swatted an 83- mph pitch over the leftfield fence for his 13th homer, which proved to be the only damage the Mets could muster in 6 1⁄3 innings against Nationals lefty Gio Gonzalez.

Harper and Jayson Werth went to the plate 10 times and totaled one out. The Mets walked 11, a stunning figure because they entered the game with only 80 bases on balls, 23 better than the next stingiest team in the National League.

“That’s not us,” said manager Terry Collins, who watched the Mets squander a bases loaded opportunity in the game in the seventh.

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Said catcher Kevin Plawecki: “It’s uncharacteristic.”

Losers of six of their last eight, the Mets need a victory tonight to avoid dropping a series to their primary competitors in the NL East.

Colon rarely gives out free passes, so his lack of command in the first inning served notice of the irregularities to come. He issued consecutive walks to Werth and Harper in the opening inning. It was the first time this season he had allowed more than one walk in a game.

Colon walked two more in a row in the third, though he didn’t get away with it this time. Former Met Daniel Murphy made it 1-0 with a hard grounder down the third-base line past a diving David Wright, who was back in the lineup one day after he was scratched with a cranky back.

Trouble found Colon in the fifth, and again it was partially self-inflicted. After a single to Werth, Harper walked for the third time. With two outs and runners on second and third, Anthony Rendon hit a two-run single through the shortstop hole to give the Nationals a 3-1 advantage.

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Moments later, Collins began his slow walk to the mound to end Colon’s 475th career start. Later, he complained that he could barely grip the ball, though he refused to blame the occasional rain that fell.

Whatever the reason, he delivered a rare stinker. Only once in Colon’s career — Aug. 6, 2000 — had he issued at least five walks and plunked a batter while working fewer than five innings.

In 3 hours, 47 minutes, Mets pitchers walked 11 batters and hit two more for only the fourth time in the history of the franchise.

Said Collins: “We’re better than that.”