It's been a blur ever since for Peterson, who was officially added to the 25-man roster on Friday after the team placed third baseman Chase Headley on the 15-day disabled list with a strained right calf.
Entering the Padres' 11-1 loss as part of a double-switch in the sixth inning, Peterson had a hit on the first pitch he saw in the seventh inning and finished 1-for-2.
"It was good, the guys in here made it very easy for me. It felt like Spring Training," said Peterson. "I was looking for a fastball to hit, and it happened to be on the first pitch."
Peterson, who was watching "Happy Gilmore" on the team bus at the time of the news, celebrated the news with his teammates. The bus was heading from Frisco, Texas to San Antonio.
"All of my teammates were just as excited as I was," he said.
Peterson is no stranger to manager Bud Black and his staff, not after appearing in 20 games during the spring when Headley was down with a strain of his left calf. Peterson played some third base and also shortstop, hitting .161 in 30 at-bats with one home run and five RBIs.
"That weighed into it quite a bit," Black said. "We liked what we saw and thought he played well at shortstop and third base. Of all the options we had [internally], this seemed the move to make."
Peterson, 23, was the 58th overall pick in the 2011 First-Year Player Draft out of McNeese State, where he also played football. He was hitting .311 with a .386 on-base percentage in 74 at-bats at the time of his promotion.
Peterson said his experience in big league camp this spring, his first, helped in terms of his development and confidence.
"I really felt like I learned a lot being around the guys," he said.
In parts of four Minor League seasons, Peterson has a .283/.376/.400 line. He's topped 39 stolen bases in each of his first three professional seasons.