The club's third-ranked prospect, who was also recently added to MLB Pipeline's Top 100 Prospects list, homered in his first plate appearance, becoming the first Reds player to do so since pinch-hitter Ted Tappe did it on Sept. 14, 1950, at Brooklyn. Clyde Vollmer is the only other Red to achieve the feat -- on May 31, 1942, at Pittsburgh.
Stephenson finished 2-for-2 with two RBIs and two runs scored, finding himself in the thick of a comeback one day after being recalled from the Reds' alternate training site.
Chicago had an 8-1 lead in the bottom of the seventh. Stephenson, who replaced starter Curt Casali for the top of the inning, stepped up to bat against Cubs reliever Duane Underwood Jr.
"[Underwood] is actually a local Atlanta guy, so it's pretty funny how it all lined up, another local Atlanta guy that I'm facing for the first time," said Stephenson, a Georgia native. "Sure enough, he throws me a first-pitch curveball and I get a fastball out over the middle of the plate and I'm on time, I hit it. And after that, I don't know what happened. It's just pretty incredible."
The ball traveled 421 feet and cleared the fence in center field.
Stephenson then singled in his second at-bat in the eighth.
In the middle of a ninth-inning rally for the Reds -- who trailed, 7-0, entering the bottom of the sixth -- Stephenson drew a run-scoring walk off Cubs closer Craig Kimbrel on six pitches to trim the deficit to 8-7. For Stephenson, who grew up watching the Braves, facing the former Atlanta All-Star was surreal.
"It was a pretty crazy moment, but you obviously have to forget about those things, especially since we had a chance to win it and stuff," said Stephenson, the No. 11 overall selection from the 2015 Draft. "That was on my mind."