WASHINGTON — The Mets’ lineup overall might have questions, but the starting outfield is exempt from such conversation.

It’s a Big Three of Yoenis Cespedes, Michael Conforto and Jay Bruce — which can potentially combine for 100-plus homers this season and carry the Mets, even if the rest of the lineup wavers.

With Conforto’s return from the disabled list, the threesome was together Thursday for the first time this season and wrecked the Nationals’ home opener. Bruce’s grand slam in the seventh inning was the exclamation point, but Conforto and Cespedes also homered, accounting for three additional runs in the Mets’ 8-2 victory before a Nationals Park sellout of 42,477.

“I would like to think we are going to be very consistent and an impactful group out there,” Bruce said, referring to the starting outfield. “I am so happy [Conforto] is back. We’ll take our outfield over most, that is for sure.”

The Mets (5-1) won their third straight and will head into Friday’s off day satisfied with their play on most levels. The starting pitching has been solid, the bullpen even better, complemented by a lineup that has produced.

Conforto returned from seven months of rehab from left-shoulder surgery and lofted a two-run homer to left in the fifth inning against Stephen Strasburg that put the Mets ahead, just as Cespedes said he predicted would happen.

“His first homer is in fact mine, because I called the homer before he hit it,” Cespedes said. “I said, ‘You are going to hit a homer to left field.’ I know Michael.”

But Cespedes’ golf shot into the left-center seats for a solo blast in the fourth was more majestic. The homer was his second in as many games and continued a trend of Cespedes crushing low pitches.

“He loves the low pitch, so you have to be careful when you throw them down there,” manager Mickey Callaway said. “You have to bounce a breaking ball to get him out, so you are kind of walking a thin line: If you don’t quite get it there and he puts a good swing on it you’re in trouble.”

Bruce connected for a towering blast in the seventh against Brandon Kintzler for his sixth career grand slam.

“I think we saw it a little bit last year, for sure: There is definitely power in the outfield,” Conforto said. “I think what we are seeing early in the season is the guys are grinding at-bats and we are seeing a lot of pitches, taking walks when we need to, keep the line moving and there is going to be somebody with thump in this lineup that they are going to run into, so I think that is big.”

Jacob deGrom (2-0) allowed two runs, one of which was unearned, over six innings on four hits and three walks with five strikeouts. The Mets bullpen followed with three scoreless frames, extending its shutout streak to 13 innings.

Conforto’s two-run homer in the fifth was initially ruled an RBI double, but a replay review showed the ball hitting behind the left-field fence before rebounding into play. Kevin Plawecki had singled leading off the inning and scored on the play.

Though the timetable for Conforto’s return had been set at May 1 during the offseason, it became evident in spring training he would be ready sooner. Callaway gave Conforto the option of beginning the season at Triple-A Las Vegas and perhaps joining the Mets next week in Miami. But Conforto said he wanted the challenge of a Mets-Nationals series to get started.

Facing Strasburg was a bonus.

“As a competitor you want to go up against the best,” Conforto said. “And they don’t get much better than him.”