Wallace, 29, ran with the opportunity after being promoted from Triple-A El Paso on June 19, hitting .302/.374/.521 with the second-most pinch-hits (15) in the big leagues in 64 games.
So impressed were the Padres that they gave him a contract for $1 million for 2016, where he'll see time at first base and provide a left-handed bat with power off the bench.
Wallace actually started to make an impact in Spring Training a year ago when he hit .391 with one home run and six RBIs, making a push for the 25-man Opening Day roster.
When he was sent to El Paso instead, he didn't sulk -- he raked.
"It's obviously disappointing anytime you don't make the team. Your goal in the spring is to make the team. But you can't control. When I went to El Paso, I tried to do something every day to prepare so that I was ready," Wallace said.
"I didn't want to go down there and sulk and squander away any chance I had."
Wallace hit .305/.380/.460 with eight home runs and 37 RBIs in 61 games before he joined the Padres in June. He just kept hitting from there, though in a different role.
Having been an everyday player for most of his professional career, Wallace took to pinch-hitting right away.
"It's definitely something where you need to find your routine," he said. "Coming up through high school, college and the Minor Leagues, you're used to playing all the time.
"But you just kind of get comfortable with it [coming off the bench] and just try to prepare daily. It was fine-tuning that early in the day and then late in the game. It was figuring out mid-inning what I was going to do to get my body ready to go. Once I got in the rhythm, I had fun with it. It was fun. ... A lot of times you had chances in big situations."
Wallace finished second to current teammate Skip Schumaker in pinch-hits, as Schumaker had 19 with the Reds. Schumaker is in camp as a non-roster invitee with a chance of making the roster.
Coincidentally, Schumaker and Wallace have lockers next to each other in the team's clubhouse here in Arizona. This isn't the first time they've met. They were teammates with the Cardinals in Spring Training 2009 when Wallace was coming up with the team.
"Skip is an awesome dude. He's a great person and a great teammate. He's had a success in a variety of roles, so anytime you get a chance to talk with someone like that, bounce concepts off each other, make each other better ... it is fun."
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.