The Mets’ youth movement took another step forward in Washington on Tuesday, when their four rookies — Francisco Alvarez, Brett Baty, Mark Vientos and Ronny Mauricio — were all in the lineup at the same time in a major league game.

The only time that had happened prior to Tuesday was on April 4 of this season, when the group was still with Triple-A Syracuse.

Two days later, Alvarez was called up to the majors. It took five months for the entire group to be reunited.

“We all came up through the organization together, waiting for this moment,’’ Vientos said at Citi Field last weekend. “I’ve grown up in the system with these guys and I’ve seen the talent across the minor leagues, and I know our players are the best of the best. I’m confident we’ll put it all together, and we hope to bring championships here. I feel like we can do that.”