Nationals’ pitcher Aaron Barrett, seen here during spring training, made his first major league appearance and got his first win on Monday.  (Photo by John McDonnell/The Washington Post)

As Aaron Barrett jogged to the middle of the diamond and into the major leagues, Ian Desmond met him at the mound. Barrett confronted a situation crucial enough to jangle a veteran’s nerves: tie game, bottom of the ninth, opening day. Desmond wanted to make sure Barrett, if only for a moment, understood where he had made it.

“Before I even start throwing my warm-up pitches,” Barrett said. “He just looked at me and said, ‘Hey, just take a second and look around. Just take this all in.’ I’m just really glad he did that, because I’ll never forget that moment that he did that for me.”

After Barrett hurled nine warm-up pitches, first baseman Adam LaRoche strode to the mound. He told Barrett to have fun, take breathes and do what he is capable of doing.

“And that’s win every pitch,” Barrett said.

Barrett threw 11 pitches, and the three Mets he blew away would tell he won most of them. In his major league debut, Barrett pitched a 1-2-3 ninth inning with two strikeouts and sent opening day to extra innings. After the Nationals won, 9-7, in the 10th, Barrett’s first appearance doubled as his first win.

“Either way, I was going to be jacked up, regardless of what the score was,” Barrett said. “Just to be in that situation, tie ballgame, and in my debut I end up getting my first win, I mean, couldn’t have chalked it up any better.

Manager Matt Williams chose Barrett over available relievers Ross Detwiler, Craig Stammen and Rafael Soriano. He likely wanted to reserve Stammen in case the game turned into a marathon and he needed a long reliever. Soriano, Williams, was available but had a chest cold. Detwiler would be used against left-handers, and three right-handed hitters beckoned.

“We have confidence in all of our guys,” Williams said. “The situation called for it. It matched up well against the guys that were coming up, we thought.”

Barrett, 26, dominated. He fired one 95-mph fastball, and he struck out Omar Quintanilla with his wicked slider, the pitch that made him unhittable as Class AA Harrisburg’s closer last season. Travis d’Arnaud popped up to the infield. Barrett finished Ruben Tejada with a slider. Tellingly, Barrett threw two sliders, and the Mets whiffed at both.

“I guess that breaking ball is alright,” said Drew Storen, who fired a 1-2-3 seventh. “It’s definitely not going to hurt us having him out there, that’s for sure.”

The Nationals may have found a late-inning weapon in Barrett. For one day, he had realized a dream. He became the 16th major leaguer to earn a win opening day in his big league debut. His parents, wife, mother in law, brother and sister in law all sat in the stands. He may have noticed them as he stood on the mound, for one split second before he helped the Nationals win a game, and gazed around at a major league park.

“I just wanted to make sure he looked at everything and saw it,” Desmond said. “Aaron and I have sat in Bible studies together. I just told him, ‘Hey man, give the glory to God. Just go out and pitch. Enjoy this man, soak it all in.’ He said thank you after the game. It was cool to be a part of it.”