Abel de Los Santos had an auspicious major league debut for the Nationals on Tuesday. (Alex Brandon/AP)

After the Nationals’ 7-2 loss to the Mets on Tuesday night, 22-year-old Abel de los Santos stood at his locker and pulled a lineup card from the top shelf. He examined it briefly — he could afford to admire it for a minute, none of his teammates were around to notice — then replaced it, just above the ball he threw for his first major league strikeout a few minutes earlier.

De los Santos made his major league debut in the ninth inning, walking the first batter before getting the last two outs,  the final one on a strikeout. He did not allow a hit and was not charged with a run, though one scored on the groundout he induced. By the time he came into the game, many of the 37,000-plus fans that filled Nationals Park were gone or on their way out. But de los Santos, a native of the Dominican Republic, had only ever pitched in front of 8,000 or so, as far as he could remember.

“The first few pitches (I was nervous),” de los Santos said. “Then I started getting into a rhythm and started to throw harder. It felt better.”

The first batter he faced in the major leagues was Lucas Duda, the Mets’ first baseman, and de los Santos threw him fastballs between 92 and 94 mph, his velocity down a bit because of nerves, he said later. He fell behind, worked the count to 3-2, then shook off catcher Wilson Ramos to throw a full-count changeup. That pitch turned into ball four, but his willingness to go to secondary stuff in a fastball count in his major league debut showed something.

“I think the bases were loaded at the time,” Nationals shortstop Ian Desmond said. “That takes … courage … to do that, shake off the catcher and do what you’re confident in. But more power to him. He knows what he wants to do, he’s confident in it, and he executed it. He made a good pitch.”

Desmond also noted de los Santos’s smile, which he flashed on the mound. Since his arrival in the Nationals clubhouse yesterday, he has used that smile to answer questions about whether or not he was surprised to be called up from Class AA Harrisburg so soon (he was), whether or not he felt nervous Tuesday night (he did, for a bit), and several other questions about the magnitude of the moment.

After Duda’s at-bat, de los Santos seemed to settle down. His velocity ticked back to 96 mph and he appeared to have command of his secondary stuff. By the time he struck out John Mayberry Jr. on a 78 mph curveball, de los Santos looked comfortable.

The right-hander is the seventh Nationals pitcher to make his major league debut this season — eighth if you count Clint Robinson, who debuted as a pitcher, though not as a hitter. He closed at times for Harrisburg, but can pitch multiple innings, and will likely slide into the middle relief role formerly occupied by Blake Treinen, at least for the time being.