ST. LOUIS -- Nico Hoerner's eyes scanned the visitors' clubhouse at Busch Stadium as he spoke Saturday morning. This was the last stop in his rookie season three years ago, and there has been a lot of change when it comes to the jerseys hanging in each locker.

"I feel like I debuted recently," Hoerner said in the hours before Chicago's 5-3 loss to the Cardinals.

"But if you look at the roster then to now and just all the people that have come through between then and now, it happens fast. Turnover's crazy, and it's true in a lot of places. It's part of this game.

"And you trust that the Cubs will continue to bring in good people. It's something they've always done a really good job of. It's out of your control, so you make the most of what's around you."

As Chicago tries to construct the "next great Cubs team," using the president of baseball operations Jed Hoyer's refrain, they are trusting that Hoerner is a key part of the blueprint. He was given the keys to shortstop this season, and Hoerner has not looked back.

"It's just Nico continuing to mature into the Major Leaguer we all thought he was and is," Chicago manager David Ross said. "He worked really hard on his body and his defense this offseason and came in to prove he could play shortstop. And he did that."

Here are three keys to Hoerner's strong season:

1. Simmons' willingness to move and mentor
The Cubs signed veteran Andrelton Simmons -- a four-time Gold Glove winner at shortstop -- with the idea of having him split time with Hoerner at short. That plan was pushed aside when a right shoulder issue kept Simmons out of the mix until the middle of May.

While he was sidelined, Simmons watched Hoerner grab hold of the opportunity. When Simmons was ready to return and share an infield with Hoerner, he did not stand in the way. He accepted a part-time role that limited him to second base and occasional innings at short.

"Seeing Nico doing really well, it's a no-brainer," Simmons said. "I think he can establish himself as a shortstop. I think his bat will play and will keep him in the league. He has speed, too. He can get better at certain things, but that comes with experience and time and reps at short."

Hoerner has appreciated how Simmons has handled the situation, especially when it comes to discussing defensive techniques for shortstop.

"He sees things, but he asks, 'Hey, what'd you think about ...'" Hoerner said. "It's never, 'This is how you should do that.' Or, he'll ask me a question about playing second base -- things like that. It's always face to face, never talking down or anything like that."

2. Rising up the defensive ranks
Chicago knew it had a Gold Glove-caliber player in Hoerner when it came to playing second base. As this season nears its fourth month, Hoerner is showing he might have what it takes to pick up that type of hardware at shortstop.

"I think he's one of the best-rated shortstops in the league right now," Ross said.

Over the offseason and through Spring Training, Hoerner put in the work to make sure his arm strength played at short. The handful of highlight-reel jump throws from deep in the hole has quieted critics on that front. And Ross was correct: Hoerner ranks near or at the top in multiple defensive statistics.

Hoerner ranks first among MLB shortstops in Statcast's Outs Above Average (nine) and is tied with Baltimore's Jorge Mateo with 8.1 Defensive Runs Above Average. His eight Defensive Runs Saved were the third-most at his position, entering Saturday.

"I see him when he's working, his focus is completely there," Simmons said. "He has a lot of upside. I think he can only get better. I don't think he's taking anything for granted. He looks like he's a guy that's going to keep working and is going to maintain this level and try to get even better at short."

3. Making most of contact-based approach
Hoerner is astute enough to know his own limitations, but he cracked a smile Saturday when asked about the "ceiling" that evaluators have tended to place on him since he broke into the big leagues.

"The concept of a ceiling is kind of silly in this game," said Hoerner, who had two hits in Saturday's loss. "I don't know what that is and I'm excited to see what it is. It's just a day-by-day thing."

Hoerner is a hitter who relies on contact, but the shortstop has been working to get the most out of those bat-to-ball skills.

Going into Saturday, Hoerner's 94.3 percent contact rate on pitches in the zone ranked fourth in baseball (min. 200 plate appearances).

Hoerner is hitting .291 on the season. His expected average of .317 is in the 96th percentile in the Majors. And across the board for ball-in-play data (contact rate, hard-hit rate, strikeout rate, average exit velocity and barrels per PA, for example), Hoerner has improved this season.

"The work has been pretty similar behind the scenes," he said. "There's a lot that comes from just the opportunity to play every day. I am just kind of accumulating at-bats, facing pitchers multiple times. All those things are very real that you guys have heard plenty of times. I think there's a lot more there still."