SAN DIEGO -- The Cubs are not looking to Nico Hoerner as a savior for a season in the balance. The highly touted shortstop prospect was not even the team's plans until 2020 at the earliest. That was before a series of setbacks necessitated an altered and expedited timeline.

Hoerner -- ranked by MLB Pipeline as the Cubs' No. 1 prospect and 47th overall -- was promoted to the Major Leagues on Monday and started at shortstop, batting sixth, in the Cubs' series opener with the Padres at Petco Park. He singled in his first at-bat on his way to a 3-for-5, four-RBI showing in a 10-2 Cubs win.

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Hoerner, selected out of Stanford with the 24th overall pick last year, is the first player from the 2018 MLB Draft to reach the big leagues. The decision to summon the 22-year-old comes with Javier Baez and Addison Russell sidelined.

“I wasn’t expecting to play today,” Hoerner said with a smile. “But fresh off the [Minor League] season, so no worries with that. No better place to be.”

To make room for Hoerner on the 40-man roster, left-handed pitcher Randy Rosario was designated for assignment.

• Here's what to expect from Hoerner in the bigs

Baez, whom teammate Willson Contreras called "the heart of this team" this week, sustained a hairline fracture in his left thumb on Sept. 1 and saw a hand specialist on Monday in Chicago. That exam confirmed the original diagnosis and ruled out any UCL damage. Baez will continue rehab work in the hope he can play in October, if the Cubs reach the postseason.

Russell, who moved into the starting role at short in Baez's absence, was hit in the head by a pitch from Brewers pitcher Adrian Houser in the third inning of Sunday's 8-5 loss to Milwaukee. Russell initially stayed in the game, but exited a half-inning later and is still under concussion protocol.

Without Baez or Russell available, utility man David Bote became the top shortstop option, with veteran Ben Zobrist next on the Major League depth chart. Bote is best suited for second or third base, while the 38-year-old Zobrist is a second baseman who has not played shortstop regularly in several years.

Enter Hoerner.

“The one thing that stands out about him,” Cubs manager Joe Maddon said, “is a lot of confidence. I don’t mean that in a braggart way. He’s just a self-confident young man. From the moment I met him, he gave me the impression that he thought he belongs here, which I love.”

Hoerner has impressed on the field and experienced a rapid ascension, even in the face of several injury setbacks.

The Cubs were aggressive with Hoerner, sending him to Double-A to start his first full professional season. On April 23, however, he was hit on the left wrist with a pitch, sustained a hairline fracture and was sidelined until late June. Hoerner hit .229/.267/.349 at Double-A in 116 plate appearances in July, but then he posted a .321/.378/.376 slash line in 119 plate appearances from Aug. 1 through the end of the Minor League season.

“I definitely want to finish strong,” he said. “It wasn’t a season that I mapped out for it to be, at the beginning of year. But I learned a lot and developed a lot.”

Overall at Double-A, Hoerner hit .284 with 22 extra-base hits, 22 RBIs, 21 walks, 31 strikeouts and a .743 OPS in 70 games. He had six multihit showings in his final eight games, hitting .378 in that stretch with two strikeouts in 39 plate appearances.

“What led us to him in the Draft in 2018,” said Cubs executive Jason McLeod, who oversees both player development and amateur scouting, “is we loved the intelligence, the aptitude of the player. He really does care about winning more than his personal stats.

“He’s athletic. There’s strength in the swing. He’s not a home run hitter, by any means, but it’s high contact with good exit velocity. We feel like he’s ready to come up here and play shortstop and hold the fort down.”

Another choice at Triple-A Iowa was shortstop Zack Short (the Cubs' No. 9 prospect), but Chicago felt Hoerner was performing better. Iowa shortstop Dixon Machado, who has four years of Major League experience at shortstop, is currently sidelined due to injury.

Last year, Hoerner was limited to 60 plate appearances across three affiliates (Rookie level and Class A) due to a left elbow injury, but hit .327 with a 1.021 OPS. Then, Hoerner opened more eyes in the Arizona Fall League by batting .337/.362/.506 in 21 games for Mesa.

The Cubs had planned on sending Hoerner back to the AFL this fall. Now, the shortstop has a chance to help the Cubs punch their ticket to the October stage.

“It’s especially unique to get a chance to debut with a team that’s trying to win,” Hoerner said. “That’s probably the most exciting part of it. Hopefully, that makes it easier for me because it’s less of a selfish situation, honestly. You go into it and you’re hoping to contribute to a win.”

Maddon’s message to Hoerner had nothing to do with postseason possibilities or filling the void of Baez and Russell.

“I just want you to go play, Nico,” Maddon said, recounting the conversation. “I don’t want you going over a lot of scouting reports. I don’t want you overthinking anything. Just play like you’ve been playing all summer. Go.”