It’s difficult to imagine where the St. Louis Cardinals would be without their rookie pitchers.

Between Carlos Martinez, Seth Maness, Trevor Rosenthal, Kevin Siegrist and Michael Wacha, the Cardinals’ young hurlers have individually and collectively played a crucial role in the team’s success this October.

However, one very important name has been absent from the mix: Shelby Miller.

Miller wasn’t just one of the top rookie pitchers during the first half of the season, he was one of the top pitchers in the game. Over his first 18 starts, the 22-year-old posted a 2.92 ERA and .225 opponent batting average with 112 strikeouts in 104.2 innings.

The Cardinals wisely offered Miller additional rest surrounding the All-Star break after he showed signs of wearing down in late June and into July. Although he had an up-and-down second half, the right-hander completed the final month of the season on a positive note by going 3-0 with a 2.76 ERA over five starts.

Miller’s season highlight came on May 10 in his home start against the Colorado Rockies, when he surrendered a leadoff single to Eric Young Jr. before retiring the next 27 hitters in order.

Since the beginning of the postseason, however, Miller essentially has been a non-factor for the Cardinals. With fellow rookie Wacha thriving in the starting rotation after a strong finish to the regular season, manager Mike Matheny relegated Miller to the bullpen for the NLDS, mostly due to his season-long struggles against the Pittsburgh Pirates

But with the beginning of the NLCS against the Dodgers, it seemed as though Miller stood a chance at starting one the latter games of the series, especially when considering right-hander Lance Lynn’s struggles in the NLDS. Starting Game 2 of the series against the Pirates, Lynn allowed five runs on seven hits over 4.1 innings as the Cardinals dropped the contest, 7-1.

Besides the aforementioned start, Lynn did pitch well out of bullpen in Game 1 of the NLCS, picking up the win in the 13-inning affair while tossing two scoreless frames.

While Miller has gotten loose in the bullpen on several occasions this October and seemed destined to get in several games, the 22-year-old right-hander has made only one appearance in the postseason thus far.

In Game 2 of the NLDS, the same game in which the Bucs chased Lynn after only 4.1 innings, Miller logged one inning out of the Cardinals bullpen, allowing one run (a solo home run) while notching a strikeout.

Even though Miller is as well rested as he’s been this season, Cardinals manager Mike Matheny decided to go with Lynn and his experience for Game 4 of the NLCS.

During Monday’s press conference, Matheny expanded on the decision:

Experience is one of your greatest teachers if you’re paying really close attention. And Lance is a guy that’s paying attention. He’s a competitor. His stuff is right. When he’s throwing the ball well, it’s fun to watch him. So hopefully he goes out there with a lot of confidence.

It’s hard to blame Matheny for going with what’s worked to this point. Plus, it’s not as though Miller helped his case to start in the series after two uninspiring starts against the Dodgers during the regular season. His second start lasted only two pitches, as he was forced to leave the game after getting smoked by a comeback line drive on the second pitch of the game.

In his only non-two-pitch start against the Dodgers during the regular season, Miller allowed three runs on seven hits and a walk while striking out three batters over 5.1 innings. Between both outings, Dodger hitters batted .296/.367/.481 against the right-hander.

Despite his lack of success against the Dodgers and limited workload in October, I can’t help but think that the Cardinals are underutilizing Miller.

When he’s at his best, he has proven to be capable of shutting down the game’s top offenses. During the regular season, 12 of Miller’s 31 starts were of the quality variety, and he struck out six-plus batters on 15 occasions.

Furthermore, Miller turned in six starts this year in which he pitched into the seventh inning. In those games, he posted a 6-0 record with a stellar 0.21 ERA and 48/5 strikeout-to-walk ratio in 43.1 innings.

Matheny seems to be reserving Miller as the team’s safety net in case one of its starters is chased from a game earlier than expected. If that scenario were to arise, then the talented rookie would undoubtedly serve as a weapon in the role.

However, if Lynn struggles in Game 4 against the Dodgers, then Matheny will be forced to consider starting Miller in his place should the Cardinals advance to the World Series.

Though Miller’s underuse this October may suggest he isn’t qualified to start a postseason, it’s more appropriate to view right-hander as the Cardinals’ non-literal ace in the hole.

The one knock on Miller is, as a pitcher who throws his fastball 70.82 percent of the time, per Brooks Baseball, he can be hittable when his command of the pitch isn’t sharp. The right-hander surrendered six or more hits in 13 starts this year and allowed 12 home runs—he gave up 20 home runs overall on the season—in those games.

However, every young hurler who throws mostly fastballs will be shelled on occasion. Therefore, it’s important to keep Miller’s success with the pitch this season in perspective.

According to Brooks Baseball’s PITCHf/x leaderboards (via Baseball Prospectus), Miller was one of four starting pitchers to throw more than 2,000 four-seam fastballs during the regular season. The others? Clayton Kershaw, Chris Tillman and Justin Verlander. Among those players, Miller ranked second with a .236 opponent batting average (against the fastball) and .387 opponent slugging percentage.

Even if Miller were to last only five or six innings in a start, he still has the potential to be highly effective and keep his team in the game. During the regular season, Miller rarely worked deep into his starts, exiting the game in the fifth or sixth innings 24 times. However, the right-hander managed to hold the opposition to three or fewer runs in 20 of those outings.

Plus, with the ongoing excellence of Cardinal relievers this October, there’s no reason for concern about handing the game to the bullpen in the sixth or seventh innings.

Read more MLB news on BleacherReport.com