Done in again by small mistakes that get magnified in a stretch such as this, the preseason NL East favorites lost for the 17th time in 22 games Wednesday to fall below .500 for the first time this late in the year since being 60-61 on Aug. 21, 2015.

This time, it was a throwing error by Adam Eaton on a sacrifice fly in foul territory and a wild pitch by Ryan Madson (2-4) in a disastrous seventh inning that dropped the Nationals to 42-43 and kept them from making up ground on the division-leading Atlanta Braves.

“We’re a good team and we’re going to go out there and compete with anybody,” said Bryce Harper, who went 0 for 4 with two strikeouts.

“We just have to keep grinding and keep doing our thing and good things will happen. We’ve never been in this position before, and I think it’s an exciting time for us. In years past, we’ve won the division by a lot of games. We’re able to be behind right now and I’m excited to get there and test it.”

Powered by struggling outfielder Jackie Bradley Jr.’s two RBIs on the sac fly and a ninth-inning double and a strong start by Eduardo Rodriguez (10-3), the Red Sox moved 30 games over .500 under rookie manager Alex Cora.

“We know where we’re at, but we still have a long ways to go,” Cora said. “(The Nationals) have a good team. They’ll figure it out. I’ve seen that before from them. They struggle a little bit and they’ll pick it up. They’ll be in the hunt.”

Bradley, who came into the game hitting .201, worked full counts on each of his at-bats that produced a run. He was hoping the ball Eaton caught deep in foul territory down the third-base line would go out of play so he could see another pitch but will gladly take the RBIs — the second time this season he has had two in a game without a home run.

“Just had to continue to battle and finally get a pitch I could handle,” Bradley said. “Any time you can help the team win, it’s a positive. It’s good, any way you can do it.”

Rodriguez struck out six in six scoreless innings, mixing his change-up and slider in more often to keep Nationals hitters off-balance.

The Red Sox now have the first pair of 10-game winners in the majors with Rodriguez and Rick Porcello, whose double off Max Scherzer helped win them the first game of this series.

The Nationals have lost four series in a row. This freefall led to the postgame meeting Wednesday afternoon.

“It’s ‘Let’s get this thing going,’” Nationals infielder Trea Turner said. “We all know we’re capable of playing better baseball. It’s time we do it. It’s do or die now.”

FEDDE HURT

Nationals starter Erick Fedde left the game one batter into the second inning with right shoulder stiffness and gave way to left-hander Matt Grace, who allowed just one hit and struck out four in four innings of relief. Manager Davey Martinez said Fedde was scheduled to have an MRI.

“We watched him throw and his (velocity) was down,” Martinez said. “He was out there and wanted to keep pitching. I went out there and they told me he was stiff and I said ‘No, we’re not going to do that to you.’”

TRAINER’S ROOM

Red Sox: Manager Alex Cora said LHP Drew Pomeranz (biceps tendinitis) would most likely make a second rehab start early next week. … RHP Tyler Thornburg was activated from the disabled list after rehabbing from shoulder surgery for thoracic outlet syndrome last June.

Nationals: 1B Matt Adams was activated after missing 16 games with a broken left index finger. To clear room, LHP Tim Collins was designated for assignment. … C Matt Wieters (left hamstring strain) is doing some catching, but still hasn’t done enough running to be ready to return.

UP NEXT

Red Sox: After a day off, LHP Chris Sale (8-4, 2.41 ERA) brings a 15-inning scoreless streak into his Friday start at Kansas City, which is expected to start Jason Hammel (2-10, 5.56).

Nationals: RHP Jeremy Hellickson (2-1, 2.63) will look to last at least six innings to spare a heavily used bullpen when Washington faces RHP Pablo Lopez (1-0, 3.00) to open a four-game series against the Miami Marlins.