The St. Louis Cardinals expected big things from their minor league system in 2021. They may not have expected so many of those big things to come from surprise contributors such as Juan Yepez and Nick Plummer.

While the Cardinals got steady performances from top prospects such as Matthew Liberatore, Nolan Gorman and Ivan Herrera, perhaps the biggest theme from the 2021 minor league season was the rapid rise of several unheralded young players who didn't even appear on Baseball America or MLB Pipeline's preseason top 30 prospect lists. Yepez and Plummer headlined a group of eye-opening standouts that included Connor Thomas, Brendan Donovan, Chandler Redmond, Matt Koperniak and a host of others. The Cardinals have a long history of turning little-known young players such as Matt Adams, Matt Carpenter, Tommy Pham and Trevor Rosenthal into valued major league contributors, and now they have a deep collection of under-the-radar prospects looking to follow in those players' footsteps.

These Cardinals minor leaguers, including several of those surprise contributors, were their clubs' most valuable players during the 2021 season:

Memphis Redbirds (Triple-A)

Hitter: INF/OF Juan Yepez — Few players in the Cardinals' system did more to improve their organizational standing this year than Yepez, who began the season in Double-A, was promoted after a dominant first month and torched Triple-A pitching for the remainder of the season. The 23-year-old slugger finished with a .286/.383/.586 slash line, 27 home runs and 77 RBIs in 111 games between the two levels. He also showcased an impressive amount of defensive versatility, playing 15 games at third base, 14 in left field and two in right in addition to 67 at first base, his natural position.

The Cardinals rewarded him by adding him to the 40-man roster and activating him for the NL wild card game. He didn't debut in the Cards' lone postseason game, but there's a very strong chance that he'll do so early in the 2022 campaign.

Pitcher: LHP Austin Warner — Warner, an undrafted free agent out of Bellarmine University who began his professional career with the independent River City Rascals, has been grinding his way through the minor leagues for half a decade. Given his 2021 performance, the 27-year-old has a great chance to finally reach the big leagues in 2022. In Warner's first full season at Triple-A — also the first in which he pitched primarily out of the bullpen — he posted a 3.34 ERA with a .213 opponent batting average, 75 strikeouts and just 22 walks in 72.2 innings. Warner displayed a couple of key qualities that should give him a solid chance of succeeding in the majors. He was very effective against both left-handed and right-handed hitters, holding lefties to a .591 OPS and righties to a .651 clip. And he did a great job of providing length out of the bullpen, throwing more than one inning in 28 of 41 outings.

Warner will be eligible for the Rule 5 Draft this winter unless he's added to St. Louis' 40-man roster. With Kwang Hyun Kim, T.J. McFarland and Andrew Miller all set to hit free agency, it should be interesting to see whether the Cardinals protect him.

Springfield Cardinals (Double-A)

Hitter: OF Nick Plummer — As much as Yepez increased his stock in 2021, Plummer — a former first-rounder who was seemingly running out of chances after hitting .199 in his first four pro seasons — did even more this season to improve his organizational stock. After a strong spring training, the 25-year-old outfielder began the season at Springfield. Plummer excelled in every area of the game, hitting .283/.404/.489 with 13 homers and nine stolen bases while playing a strong defensive center field in 90 Double-A games. Plummer was promoted to Memphis for the final month of the season and continued to rake, posting a .267/.455/.440 slash line with two home runs and four steals in 27 games.

Plummer was part of the Cardinals' taxi squad for the NL wild card game, and since he needs to be protected from the Rule 5 Draft, he has a great chance of being added to the 40-man roster this offseason and making his major league debut at some point in 2022.

Pitcher: RHP Ramon Santos — Santos, a Dominican native who signed with the Cardinals as a 17-year-old, has endured a steep climb up the minor league ladder. He didn't graduate to full-season ball until his sixth professional season. After spending the bulk of the 2018 season in Double-A, he was sent back to High-A the next year, missed the entire 2020 season due to the COVID-19 pandemic and started this season in Low-A. Following six impressive relief outings with Palm Beach, Santos was bumped up two levels to Springfield and excelled. Like Warner, Santos pitched well in a multi-inning relief role, throwing 61.1 frames over 29 Double-A outings. He posted a 2.79 ERA and did a great job of missing bats, holding opponents to a .164 batting average while striking out 96 and walking 39. Santos received a late-season promotion to Memphis and was unscored on in three of his five appearances, though a pair of disastrous outings inflated his Triple-A ERA to 12.46.

Santos, 27, will be a free agent this offseason. Thanks to his performance this year, he should have a variety of suitors, and while it may not be with the Cardinals, he has a chance to make a serious push for a promotion to the big leagues as soon as next year.

Peoria Chiefs (High-A)

Hitter: 3B Jordan Walker — Walker, 19, was already firmly on the radar after the Cardinals selected him in the first round of the 2020 draft, but he established himself as one of the elite hitting prospects in all of baseball this season. The teenager tore the cover off the ball in the Low-A Southeast league, hitting .374/.475/.687 with 11 doubles, a triple and six homers in 27 games before his promotion to Peoria on June 29. While Walker wasn't quite as dominant in High-A, he was still the best hitter on the team — a pretty impressive feat for a player who is still two years away from legal drinking age. In 55 games with the Chiefs, Walker posted a .292/.344/.487 slash line with 14 doubles, three triples, eight homers and eight stolen bases.

Since he's so young, there's a possibility that the Cardinals may send Walker back to Peoria to begin 2022, but even if they do, he should reach the upper minors at some point next year if he continues to hit like he did this season. That promotion would continue a remarkable ascent for Walker, who was in high school just over a year ago.

Pitcher: RHP Wilfredo Pereira — Pereira, 22, began the season in the Chiefs' bullpen and struggled a bit, posting a 4.78 ERA over 16 relief appearances. But something clicked when he moved into Peoria's rotation on July 7, and he was dominant the rest of the way. In 13 starts, Pereira threw for a 2.62 ERA with a .209 opponent batting average, 74 strikeouts and 25 walks in 65.1 innings. Overall, he finished the year with a 3.33 ERA, 115 strikeouts and 40 walks over 97.1 frames. While he's somewhat undersized (5-foot-11 and 197 pounds) and doesn't have a ton of velocity, Pereira was extremely consistent out of the rotation this year and has made himself one of the organization's more intriguing starting pitching prospects. He'll likely begin the 2022 season in Springfield and get a chance to prove that he has what it takes to succeed in the upper minors.

Palm Beach (Low-A)

Hitter: OF Matt Koperniak — Koperniak, 23, was one of the best stories of the Cardinals' minor league season, playing at three levels in his first year as a pro and finishing at Double-A. Koperniak, who signed with the Cardinals last summer after going undrafted out of Division III Trinity College, spent most of the season at Palm Beach and stood out at the plate, hitting .322/.443/.470 with 15 doubles, four homers and nearly as many walks (30) as strikeouts (32) in 58 games. Koperniak was promoted from Palm Beach to Peoria on Aug. 1, and after going 6 for 14 with three doubles in High-A, he was part of the wave of players promoted to Double-A on Aug. 10 in the wake of Springfield's COVID-19 outbreak. While he wasn't quite as prolific offensively after reaching the upper minors, he still posted a respectable .271/.326/.391 slash line with three homers in 33 Double-A games. Koperniak will probably start the 2022 season back at Springfield, but after beginning 2021 with extremely slim odds of ever reaching the major leagues, he's increased those odds exponentially in just a handful of months.

Pitcher: RHP Dionys Rodriguez — The 21-year-old Rodriguez didn't make his 2021 debut until the beginning of June, and he didn't enter Palm Beach's rotation until July 8. But whether he was starting or relieving, the 6-foot, 188-pound right-hander was remarkably consistent this season, posting a 3.36 ERA with a .201 opponent batting average, 88 strikeouts and 22 walks in 69.2 innings spanning 22 appearances (12 starts). Three of those starts were scoreless, and he allowed two or fewer runs in another six of them. Rodriguez might have earned an in-season promotion to Peoria if not for his late start, and he'll almost certainly receive one to begin the 2022 campaign.

Florida Complex League (Rookie)

Hitter: OF Luis Montano — Montano, a 19-year-old Dominican native, struggled after moving stateside in 2019, posting a .584 OPS in rookie ball. After missing the 2020 season due to the pandemic, Montano put it all together in 2021, hitting .275/.341/.492 with 10 doubles, two triples and four homers in 35 games for the FCL Cardinals. While it's a small sample size and Montano is a bit old for the FCL, the left-handed-hitting outfielder likely showed enough to earn a promotion to full-season ball in 2022.

Pitcher: RHP Jose Davila — Davila, the top pitcher in the Cardinals' 2019 international signing class, put together a very strong showing in his first professional season. While the 18-year-old struggled to keep his head above water in four early-season relief appearances with Palm Beach, he was much more in his element once he reemerged with the Cardinals' FCL affiliate. In 11 games (nine starts) at the rookie level, Davila posted a 3.77 ERA with a .201 opponent batting average, 49 strikeouts and 24 walks in 45.1 innings. The Venezuelan right-hander is still extremely young, but perhaps he'll fare better if given another opportunity with a full-season club next year.

Dominican Summer League (Rookie)

Hitter: OF Felix Taveras — Taveras, 18, thrived in his first pro action, hitting .301/.369/.549 with nine doubles, three triples, six homers and seven stolen bases in 39 games. The left-handed hitter wasn't a high-profile international signing, but he made about as strong of a first impression as a player can make.

Pitcher: RHP Benjamin Arias — After struggling to an 8.39 ERA over 18 games in 2019, his first professional season, Arias took the league by storm as he returned to action this year. In 12 starts, the 19-year-old right-hander posted a 1.94 ERA with a .204 opponent batting average, 61 strikeouts and 14 walks over 51 innings. The 6-5, 195-pound right-hander's outstanding season likely puts him in position to move stateside and pitch in the FCL in 2022.

For the purpose of these rankings, players are listed at the level where they spent the majority of the season.

Top photo of Juan Yepez courtesy of Memphis Redbirds.