The 24-year-old Piscotty, called up from Triple-A Memphis before the game, batted ninth and played left field.
"I've really tried to push it out of my mind as best I can," Piscotty said before the game, "but now it's finally here, so I'm excited and ready for it."
The right-handed hitter was batting .272 with 11 home runs and 41 RBI in his 87 games at Memphis. He has raised his season average from .243 since June 1 by batting .308 (44-for-143) over the past six weeks.
The 6-foot-3, 210-pound graduate of Stanford was chosen for the Pacific Coast League All-Star team in 2014. Piscotty credits his recent hitting improvement to swing changes he made last winter while working with coaches at Stanford as he completed his degree in atmosphere and energy engineering.
"From the numbers perspective, there's been some noticeably good changes," Piscotty said. "In spring training it was a little rocky for me, and even the first month in Triple-A was pretty rocky.
"But I really felt that I had some potential that was untapped and really wanted to kind of see if it was there," he added. "It was a big risk, no doubt about it, but I'm very pleased that I took the risk."
The Cardinals optioned outfielder Tommy Pham to Memphis on Sunday to make room for Piscotty on the 40-man major-league roster.
Information from The Associated Press was used in this report.