WASHINGTON — Seth Lugo was the Mets’ most dominant pitcher Thursday — albeit in a short burst.

Summoned to pitch the seventh inning, the right-hander struck out all three batters he faced in the Mets’ 2-0 Opening Day victory over the Nationals.

Lugo was just parroting what he had seen from starter Jacob deGrom, who struck out 10 batters over six shutout innings.

“I’m out there watching everything [deGrom] does and he kind of set up the game for me and for everybody,” Lugo said. “I just kind of went out there and did what he did, so that is a good feeling today.”

Lugo emerged as a key bullpen member last season, when he appeared in 49 games as a reliever and posted a 2.30 ERA. Manager Mickey Callaway’s ideal alignment has Lugo, Jeurys Familia and Edwin Diaz for the final three innings. All three were on display Thursday.

“Watching [deGrom’s] pitch count, I had a pretty good feeling that I would be coming in,” Lugo said.

Dominic Smith pinch hit in the eighth, and Keon Broxton entered as a pinch runner for Pete Alonso in the same inning. Broxton then went to right field for the ninth inning as a defensive replacement for Michael Conforto, providing a glimpse of how he might be used this season.

Smith walked against Max Scherzer and scored the Mets’ final run of the game.

“To be able to put Dom in to draw that huge walk so we could score that second run, get Scherzer out of the game, that is big,” Callaway said. “We have some weapons and of course the defense out there. It’s great to have weapons off the bench and be able to make moves like that.”

DeGrom became the 27th different pitcher to start a Mets season opener. Tom Seaver holds the franchise record with 11 starts on Opening Day.