Less than 24 hours after Matt Harvey won a pitcher’s duel against Washington ace Stephen Strasburg, the Mets’ staff didn’t exactly follow the lead of their first-year phenom.

They squandered a five-run inning, allowed home runs to Ian Desmond, Adam LaRoche and two to Bryce Harper and watched the scoreboard light up behind them on the way to a 7-6 loss to the Nationals yesterday at Citi Field.

Harper’s second homer was propelled into the bullpen off Josh Edgin to to break a tie in the eighth inning and send Washington to victory.

“I made a bad pitch,’’ Edgin said. “I was trying to go away and it ran back in on me. Bad pitch — kudos to him, he hit it.’’

There was plenty of blame to go around, from starter Jeremy Hefner, who allowed three runs in just four innings, to the bullpen, which coughed up four more runs in five frames. The starters not named Matt Harvey are 6-6 with a 5.95 ERA, and a team that was crisp and energetic Friday showed frailty yesterday.

They took a 5-3 lead in the fourth inning off Gio Gonzalez, only to have Aaron Laffey surrender a three-run homer in the next inning.

“You get five against Gio, we’ve got to win that game,’’ said David Wright, who had a triple and two walks. “If you get some momentum on your side, we’ve got to find a way to go out there and put up zeros. And we weren’t able to do that.

“That’s what good teams do. They give up some runs, they find a way to get them right back.’’

Hefner has allowed 11 runs and six homers in just eight innings over his past three appearances. Mets manager Terry Collins said inconsistent work has led to Hefner’s sinker being inconsistent. Either way, Hefner has to keep his pitches down and the ball in the park.