WASHINGTON -- Nationals lefty DJ Herz released a large exhale while he warmed up ahead of a very big Tuesday night. He was going up against an experienced Mets lineup in his Major League debut.

“He’s got good stuff, we told him to just attack the strike zone,” manager Dave Martinez said before the game. “Hopefully, he goes out there and just competes.”

Herz competed. He marked the beginning of his Major League career with his first strikeout of three-time All-Star Pete Alonso in front of family, friends, and coaches who had made the four-hour drive from his hometown of Fayetteville, N.C.

The Nationals’ No. 12 prospect, per MLB Pipeline, continued to work through four-plus frames. Once his night was over, he walked back to the dugout while receiving a standing ovation in Washington’s eventual 6-3 loss at Nationals Park.

Herz, who was called on to start after Trevor Williams landed on the 15-day IL with a right flexor strain, allowed four runs on seven hits and two walks to go with three strikeouts.

The more experience Herz got throughout the game, the more comfortable he felt to go out there and do his thing. In three scoreless innings to begin his debut, Herz retired seven straight batters.

“The adrenaline was up there in the first inning,” Martinez said. “Once he settled in and threw a strike, striking out a big guy like Alonso, he kind of settled in a little bit, and then he was around the plate.”

With two outs and the bases loaded in the top of the third, the southpaw had to get himself out of the jam. Herz offered up three consecutive fastballs in whiffing All-Star J.D. Martinez. The third was right at the knees, freezing the veteran hitter to end the inning.

An 87.7 mph cutter ended the 23-year-old’s scoreless outing. With one out and a 1-2 count, Harrison Bader capitalized on Herz’s offering for a two-run homer to give the Mets a lead in the fourth inning.

“We beat him on the slider in the first at-bat. I think [the cutter] was the right pitch,” Herz said. “I just think I left it over the plate a little bit too much. Probably should’ve gone a bit more inside.”

With runners on first and second and none out in the fifth, Martinez took the ball from Herz. The manager said he wanted to keep Herz to around 80 pitches as he threw 75 (48 strikes).

“I told him, ‘Hey, you did it, you did a really great job today. You really, really did so let’s focus on the positives,’” Martinez said.

Before his callup, Herz logged 42 strikeouts in nine starts with Triple-A Rochester. He ranked first in opponents’ average (.176) in the Minors. Herz was acquired by Washington at the 2023 Trade Deadline, along with shortstop and No. 19 prospect Kevin Made, from the Cubs in exchange for Jeimer Candelario.

Herz received the call that he was heading to the Majors while driving to Worcester, Mass., where Rochester was set to begin its next series. He called his girlfriend, family, friends and tried to get some sleep before flying out to Washington D.C.

“I probably let out a scream like, ‘Let’s go!” Herz said. “I drove all the way to Worcester, I had to get my baseball bags. Then, I went to sleep. It was hard to sleep, but I slept and then flew in this morning.”

Herz became the fourth National to make his debut this season, following No. 16 prospect Trey Lipscomb, Mitchell Parker and Nasim Nuñez. Now that he’s got his first game under his belt, Herz said he can only think about moving onto the next.

“It was an awesome first day,” he said. “I’m kind of tired right now, but it was a great day. It was a lot of memories and my family loved it. I know they’re proud so I’m happy.”