WASHINGTON — Rick Porcello hit a three-run double off former teammate Max Scherzer and allowed two runs in six innings to power the Boston Red Sox to a 4-3 victory over the Washington Nationals in the opener of their three-game interleague series Monday night.

Porcello’s first major league extra-base hit came in the second inning on an 0-2 pitch after the Nationals intentionally walked Jackie Bradley Jr. to pitch to him. His .156 batting average in just 35 plate appearances made it appear to be the right calculation, but Porcello drove Scherzer’s 96 mph fastball over the head of Juan Soto in left center for his first RBIs since 2009.

Scherzer and Porcello were teammates for five seasons with the Detroit Tigers.

On the mound, Porcello (10-3) struck out five and limited the damage to solo home runs by Anthony Rendon and Daniel Murphy. Scherzer (10-5) struck out nine and kept the Red Sox off the board except for Porcello’s bases-clearing double and became the 11th pitcher to reach 1,000 strikeouts with two different teams.

When Scherzer exited the game after 108 pitches, Mookie Betts provided the Red Sox with their insurance run with a solo shot off Brandon Kintzler in the seventh, his 21st home run of the season. Bryce Harper hit his 21st in the eighth, but Boston’s bullpen held on.

Craig Kimbrel got into some trouble but picked four outs for his 25th save in 27 chances.

FIRST-BASE HARPER?

Harper is doing just fine in center field but on Monday fielded some grounders at first base. It’s just experimental for now but could help the Nationals out down the line.

“That’s kind of him getting outside of his comfort zone and letting him do something different,” Manager Davey Martinez said. “I don’t ever know if he’ll ever start a game there, but I believe that if we’re in a pinch and we’ve got to make some kind of decisions in-game, he probably could play there.”

PUERTO RICO PRIDE

Martinez and Red Sox manager Alex Cora were never on the same team but knew each other well from their playing days. They exchanged lineup cards as two managers of Puerto Rican descent in the series opener, a special moment and occasion for them.

“It’s pretty cool,” Martinez said. “It’s good for Puerto Rico, it really is. And I know he feels the same way I do. We feel blessed and we’re happy we got the opportunity to do what we do.”

TRAINER’S ROOM

Red Sox: RHP Steven Wright (left knee inflammation) received a PRP (platelet-rich plasma) injection, a day after throwing a short bullpen session. Cora said Wright could return before the All-Star break. … 2B Dustin Pedroia (left knee inflammation) will remain in New York all week. “They still feel that structure-wise, there’s nothing wrong as far as the surgery,” Cora said. “He’s going to keep doing certain tests with the doctor and see where they’re at.” … Cora said RHP Tyler Thornburg (shoulder surgery) will most likely be activated from the disabled list during this series.

Nationals: 1B Ryan Zimmerman (right oblique strain) took part in a simulated game as he prepares to try to play in a game for the first time since May. “I got some swings off two kids who were gracious enough to come here and throw in 110-degree heat,” Zimmerman said. … Martinez said C Matt Wieters (left hamstring strain) will go on a minor-league rehab assignment Tuesday at Double-A Harrisburg after reporting significant progress in the simulated game and could be activated as soon as Wednesday.