PHOENIX -- The D-backs called up top prospect Alek Thomas from Triple-A Reno on Sunday, then immediately put him in the starting lineup for their 4-0 win in the series finale against the Rockies at Chase Field.

Thomas started in center field and batted eighth, going 1-for-3 and recording his first career hit with a leadoff double in the fifth inning. He later came in to score when Colorado starter Germán Márquez committed an error on a pickoff throw to first base.

"I was a little nervous, obviously," Thomas said. "I've been nervous since [Saturday], so I think it was a crazy relief to get that first hit out of the way, and it felt really good. That was one of the better swings I've had this year."

Thomas, the No. 18 overall prospect in baseball per MLB Pipeline, was Arizona’s second-round pick (No. 63 overall) in the 2018 Draft out of Mount Carmel High School in Chicago. He hit .277 (28-for-101) with eight doubles, one triple, four home runs and 14 RBIs over 24 games with Reno in 2022.

"I've been waiting for this moment for a while," Thomas said. "So really excited to be here."

Here are some questions (and answers) about the decision and what it means going forward.

Why promote Thomas now?
With catcher Carson Kelly going on the injured list due to a Grade 1 left oblique strain, Daulton Varsho slides from center field to being the D-backs' primary catcher. That opened a spot in center, and Thomas' recent performance in Triple-A made him the guy.

In particular, it's Thomas' patience and approach at the plate that impressed the organization. After walking four times in his first 16 games this year, Thomas drew nine walks over his last eight games with Reno.

"He's played well down there," Arizona general manager Mike Hazen said. "He's walked like nine times in eight days and been pretty consistent with that part of the approach. That was something we sent him down there with [out of Spring Training], and he's done a good job. He's played elite center field."

How much playing time will Thomas get?
D-backs manager Torey Lovullo likes to get players who are called up right into a game so they don't have to sit around and let their nerves build up.

In Thomas' case, he figures to be the everyday center fielder, at least until Kelly comes back from the IL.

"He'll get a little runway here to go and show us what he can do," Hazen said. "His talent is one of the best in our system, and he's gone out in the Minor Leagues and performed at every step of the way. And now, he'll get a chance to do it up here."

How did Thomas get the news he was coming up?
Thomas was scheduled to have off Saturday night, and just before Reno's game, manager Gil Velazquez told Thomas he was headed to Phoenix.

"It was all crazy," Thomas said. "I didn't really know how to act at first, but once I got on the plane, it started all setting in."

Who was Thomas' first phone call after he got the news?
"I texted my girlfriend and called my dad," Thomas said. "He didn't answer, he was walking the dog. So I called my mom and she answered and I was like, 'Come on, you've got to get dad on the phone.'"

Thomas' dad, Allen, worked for 27 years as the strength and conditioning coach for the White Sox.

What does this mean for Varsho?
In the short term, Varsho will get his starts behind the plate, but that doesn't mean that will be his long-term home.

Varsho has been one of the D-backs' best offensive contributors so far this year, and he is an outstanding defender in center. In the outfield, he can be in the lineup more because catchers do not play nearly as much. And right now, he's carrying a big part of the offensive load.

"I think that there's probably some decision that could get made there," Hazen said. "But we'll see. I'm hoping that our offense is going to build to the point where it's robust enough that we can handle having him down two days a week. But he is probably one of our best -- if not, right now, our best -- offensive player."

Arizona still believes in Kelly, despite his struggles at the plate this year. So even if Thomas plays well and sticks in the big leagues, Varsho could find some playing time at one of the outfield corners.