WASHINGTON — John Maine has had better days, and the same goes for the Mets.
Both were so awful here last night that even the Nationals — otherwise known as the worst team in baseball by a mile — had no problem strolling to a 7-1 win at Nationals Park.
At least the latest Mets’ misery on what has become an unexpected road trip from hell didn’t last long as Long Island native John Lannan needed just two hours to polish off his first career complete game.
The Mets have now dropped four of five on this week-long trek to bottom-feeders Pittsburgh and Washington, and this was easily the worst of the lot.
When the 15-39 Nationals — on pace to challenge the 1962 Mets for the worst record ever — weren’t bashing Maine’s batting-practice fastball, Lannan was mowing down what amounted to a Triple-A lineup from Jerry Manuel’s injury-ravaged club.
While Washington was hitting three homers off Maine (5-4), the Mets were hitting into a Nationals-record five double plays that included one of the oddest you’ll ever see in the fourth inning.
“Not a good night,” said Manuel, who got another unexpectedly horrific outing from a proven starter after Mike Pelfrey’s meltdown in Pittsburgh on Thursday.
The biggest concern for the Mets last night was Maine, who was making his first start since being socked with a severe case of stomach flu that caused him to leave early from his previous outing.
Maine usually dominates the Nationals, posting a career 7-2 record against them coming in, but he was pitiful last night.
Maine made it through just four innings, giving up all seven Washington runs on six hits and two walks. That included three no-doubt-about-it homers by Adam Dunn, Nick Johnson and Elijah Dukes.
“John Maine might be going through a period of dead arm or whatever,” Manuel said. “I just didn’t see the electric stuff we’ve been known to see, and that’s a little concerning when that happens.”
Maine, who lost for just the second time in his past seven decisions, admitted his velocity is down but offered no excuses after lasting just 68 pitches.
“I had nothing today,” Maine said. “I mean, it was awful. It was a waste of a day. I didn’t have my legs under me. I tried to get something out of my fastball, but I didn’t have it. It’s a bad feeling. It’s terrible.”
Maine also admitted he wasn’t at full strength physically after being laid up with the stomach virus most of this week.
“I’m not 100 percent, but I wanted to go out there and pitch,” Maine said. “It was my fault. I made bad pitches.”
While Maine was scuffling, Lannan was cruising. The left-hander, who began the night 2-5 thanks mostly to a season-long lack of run support, showed what he can do when finally given some backing.
The Mets hit into double plays in each of the first four innings — with the capper a bizarre twin-killing that saw Emil Brown called out for running past Luis Castillo in the fourth — then went down meekly until breaking through for an unearned run in the eighth.
Lannan induced 19 ground-ball outs by the Mets, who saw the top four hitters in their depleted lineup go a combined 1-for-13.
“He kept the ball down, they got a lot of double plays,” Manuel said. “It was a simple as that.”
Unfortunately for Manuel, nothing seems very simple for his own team these days.
bhubbuch@nypost.com