Manager Joe Maddon wanted Contreras matched up with veteran John Lackey, whom the young catcher caught on Friday during a side session.
"John's going to have to be more proactive in regards to leading Willson to what he wants to do," Maddon said.
The two worked well together, and Contreras drove in a run with an RBI single in the third.
"He was pretty excited," Lackey said of Contreras. "The talent is there, for sure. Things are going to slow down for him. It'll get better. It was a good first step."
The plan for now is to continue to carry three catchers, and have Contreras start at least two games a week. The Cubs know there will be growing pains.
"Let him go play," Maddon said of Contreras, the team's Minor League Player of the Year last season. "If he makes a mistake, he'll make it. I know it'll be an aggressive mistake. ... If you see Johnny [Lackey] call him out to the mound, there might be something going on there. I have a lot of faith in the guy."
Before the first pitch, Contreras said he'd be calling the shots then added, "but I don't know if he's going to throw it." Lackey and Contreras did have a few conversations in-game, but it was a good starting debut for the 24-year-old catcher.
"That had some hair on it and it was absolutely accurate," Maddon said. "You look into the crystal ball in the future, and you'll see a lot more of that. He's a game changer where the other team won't go."
Contreras' family can't wait to see what happens. He said the response to his first at-bat was "insane."
"It was amazing," Contreras said. "I have no words to explain how happy I was."
He did get Sunday's home run ball from the fan who caught it in the bleachers. Contreras talked to his parents, who cried with joy, and his older brother Willmer, 27, and younger brother William, 17, who is playing for the Braves' rookie league team. Yes, two L's in the boys' names.
"My mom and dad wanted us to be special," Contreras said.
Carrie Muskat has covered the Cubs since 1987, and for MLB.com since 2001. She writes a blog, Muskat Ramblings. You can follow her on Twitter @CarrieMuskat and listen to her podcast. This story was not subject to the approval of Major League Baseball or its clubs.