"That first pitch," said Peterson, "I was a little nervous."
Peterson stepped out. He took a deep breath.
"I stepped back in and that was it," said Peterson.
He hasn't looked back since.
The Mariners' first-round Draft pick in 2013, Peterson, who plays both first and third base, spent the first half of this season reaffirming all the positive things that prompted the Mariners to take him with the 12th selection and sign him to a $2,759,100 bonus.
Seattle initially selected him in the 33rd round when he came out of high school in 2010, wanting to keep the door open if he was interested in signing but well aware he was planning to attend college.
After opening the season at Class A Advanced High Desert, where he hit .326 with 18 home runs and 73 RBIs in 65 games, Peterson was promoted three weeks ago to Double-A Jackson, where he has hit .290 with three home runs and seven RBIs in 15 games.
And then, along with former High Desert teammate Gabby Guerrero, Peterson was selected to play in the SiriusXM All-Star Futures Game on Sunday at Target Field. Peterson started at first base for the U.S. Team and was 1-for-2 with a double, while Guerrero, the starting DH for the World Team, was 0-for-2 with a strikeout.
It's a long ways from 10 months ago, when Peterson was hospitalized for two weeks after being hit by the pitch, and then was barred from any baseball activities for three months.
"I had so much down time recovering from the injury to think about what I needed to do when I came back to be a better player," he said. "I missed out on some things, fall ball, an invite [to big league Spring Training], which was understandable."
Peterson, however, hasn't missed a step on the field.
"It was brutal," he said of the recovery. "But it showed me that I wanted this even more than I did before. It was a setback that gave me the time to realize this is what I want."
The only lingering reminder of that night last August, when he took a fastball from Wisconsin Rapids right-hander Jorge Lopez to the jaw, is the special flap on his helmet that protects his left jawline when batting. It is similar to the flap Atlanta outfielder Jason Heyward is wearing after being hit in the face by a pitch from Mets left-hander Jon Niese last August.
"It has taken a little getting used to," he said of the flap, "but it's part of what I have to deal with to accomplish what I want to do."
And playing baseball is what Peterson has wanted to do for as long as he can remember. Oh, he also played basketball and football at Gilbert (Ariz.) High School, but that was more to keep busy than anything else.
"Baseball was always my sport, and the only scholarships I was offered were for baseball," said Peterson, who spent three years at the University of New Mexico before signing with the Mariners.
Guerrero also has been focused on baseball seemingly since he was born. The nephew of former big league outfielder Vladimir Guerrero and infielder Wilton Guerrero, Gabby said baseball was the focus of the family.
"There was nothing else," he said when asked what options he had when he signed with the Mariners as a 17-year-old in 2011. "Baseball was my plan from when I was little."
It didn't hurt to have his uncles around in the winter to tell him about living that big league dream.
"They were big influences," he said. "We would talk hitting, but we also would talk about what to expect off the field. They helped me understand what would happen."
Guerrero, like Peterson, learned his lesson well.