The 23-year-old right-hander said he could barely contain his emotions as he made his way from the bullpen to the mound.
"You can't really explain it," Jenkins said. "My heart was pumping through my chest."
Jenkins was tested early. The first batter he faced, Adeiny Hechavarria, dribbled a ball softly toward the third-base side. Without hesitation, Jenkins scrambled forward to it and fired to first for the out.
"I was just making sure I didn't squeeze the ball too hard and throw it into the stands, if anything," he said. "Just make sure I got the ball to Freddie [Freeman] and got that out. That was big. That kind of got me going. I was really excited."
Jenkins finished the inning by sandwiching a Marcell Ozuna single between two more weak groundouts, but what caught Braves manager Brian Snitker's attention was Jenkins' fastball velocity to his last batter, Miguel Rojas.
After his fastball sat in the 92-93-mph range to his first few hitters, Jenkins pumped it up to 96 to Rojas, who could barely catch up to the heat.
"That was kind of what I was looking for," Snitker said. "Overall, I liked what I saw. I've never really seen him out of the stretch, exclusively, because I've just seen him as a starter. Thought it was OK."
Jenkins said the slight spike in velocity was simply a product of getting loose, something he's had to do more quickly now that he's in the bullpen.
"Usually I kind of get loose toward the second or third inning," he said. "Bullpen life's a little bit different. The fact that the fastball had a little life on it today was pretty big. I'm glad I had a clean inning, and I'm glad I kept us in the game."
A first-round pick by St. Louis in 2010, Jenkins came to Atlanta along with Shelby Miller in the Jason Heyward trade in Nov. 2014. He was called up this season from Triple-A Gwinnett on June 16 after going 6-3 with a 2.91 in 14 appearances this season, nine of which were starts.
Pitching across seven seasons in the Minor Leagues after being drafted, Jenkins was glad to make his debut in a low-leverage situation.
"Obviously, you don't want to come in your first time in a really close game or something like that," he said. "I knew what Snit was doing the whole time, him and Roger (McDowell) kind of getting me my first inning in a low-leverage situation. They did and I'm just glad I got to put up a zero."