Although only 10 teams get to participate in the exclusive postseason dance and just two make it to the World Series, many more clubs will provide their fans with meaningful games late into September this season. 
While these postseason contenders were good enough to stay in the hunt this year, they each have one youngster who could prove to be especially vital to their success -- and the success of fantasy owners alike -- in 2018. 
The following 16 players -- each no older than 25 -- deserve special attention, as they could be set to make a sizable leap forward next season. While some have already made waves in the Majors and others have yet to find their footing, all are on the upswing. 

Trea Turner, shortstop, Nationals
On a Nationals squad stocked with productive veterans, Turner stands out as one of the few youngsters who can contribute heavily to their winning ways. While the speedster certainly has been a coveted fantasy asset at times during his big league career, he has yet to put together a full campaign of sustained excellence. With improved health in 2018, Turner could be a top 10 overall asset who compiles at least 15 homers, 65 steals and 110 runs scored. 
Corey Seager, shortstop, Dodgers
While Seager has already emerged as a reliable fantasy performer and a National League MVP Award candidate, he may be capable of raising his game to an even greater level. After increasing his fly-ball and hard-hit rates this season, the 23-year-old could be on the verge of producing 35 homers and 100 RBIs next year. 
Kaleb Cowart, second baseman/third baseman, Angels
In a veteran-laden organization, Cowart is one of the few players who could add a youthful presence to the Angels' 2018 lineup. Having shown multidimensional plate skills and plus speed in Triple-A this year, the 25-year-old could be a five-category asset if he secures a regular role with the big league club. 

Rafael Devers, third baseman, Red Sox
Devers skyrocketed through the Minors, playing just 77 games in Double-A and nine contests in Triple-A before reaching the Majors at age 20. The youngster was not fazed by playing at baseball's highest level, going deep in his second big league game and becoming a key contributor for a Boston club that was in desperate need of stability at the hot corner prior to his arrival. With improving power and solid contact skills, Devers could hit .300 with 30 long balls during his first full year in the Majors. 
Ian Happ, outfielder/second baseman, Cubs
Like Devers, Happ raced through the Minors, joining the Cubs as a 22-year-old after playing 65 games in Double-A and 26 contests at the Triple-A level. Although the youngster endured the typical inconsistency of a first-year player, he flashed enough power and speed to suggest that he could produce 30 homers, 85 RBIs and 15 steals as a regular member of a talented lineup in 2018.
Byron Buxton, outfielder, Twins
The No. 1 prospect in baseball (via MLBPipeline.com) prior to the 2014 season, Buxton has many times disappointed optimistic fantasy owners during the past three years. But the 23-year-old is one of the fastest players in baseball, and he is slowly developing the necessary plate skills to earn regular opportunities to swipe bases. With continued improvements, Buxton could compile 15 homers and 35 steals next year.

Lewis Brinson, outfielder, Brewers
While Brinson did not turn heads in his brief opportunities with Milwaukee this season, he has produced outstanding results in Triple-A and could be a post-hype sleeper in 2018 drafts. As the center fielder on an improving Brewers squad, the 23-year-old has the potential to be a five-category asset who logs a 20-20 campaign. 

Bradley Zimmer, outfielder, Indians
Given the dearth of speedy players who also possess notable power skills, Zimmer was a breath of fresh air for fantasy owners after his in-season callup in 2017. By making some adjustments at the plate and lowering his strikeout rate, the 24-year-old could produce more than 20 homers and reach base enough to record 30-plus steals next season. 
Derek Fisher, outfielder, Astros
Like Zimmer, Fisher demonstrated an exciting blend of power and speed in the Minors, compiling 42 homers and 44 swipes across 950 plate appearances during 2016-17. Moreover, the outfielder did not look out of place when given a chance to contribute to a potent Astros lineup down the stretch this year. With a full-time role next season, Fisher could go 20-20 and drive in at least 80 runs. 
Nomar Mazara, outfielder, Rangers
Sure, Mazara did not take a notable step forward in his second season after a solid rookie campaign in 2016. But the 22-year-old has still managed to hold his own in the Majors for two straight years at an age when many of his peers are still trying to reach The Show. By making strides against southpaws and continuing to increase his fly-ball rate, Mazara could hit .280 with 25 homers next year. 
Jorge Bonifacio, outfielder, Royals
Bonifacio proved to be an unlikely savior for the Royals, logging an .825 OPS during April and May before his veteran teammates got on track and carried the team the rest of the way. Though he was relegated to a lighter role after the club acquired Melky Cabrera in July, the 24-year-old has shown that he could be a 30-homer contributor with a regular spot in a lineup that may undergo an overhaul this offseason. 

Raimel Tapia, outfielder, Rockies
A strong contact hitter who has thrice topped the 20-steal mark in the Minors, Tapia has fared well in limited big league action so far. Looking ahead to 2018, the 23-year-old could be a source of batting-average help as well as 25-plus stolen bases if he earns a regular spot in a lineup that typically ranks among the most productive in baseball. 
Jordan Montgomery, starter, Yankees
Montgomery was a stabilizing presence in the Yankees' rotation during the initial three months of the season, going 6-4 with a 3.53 ERA and an 8.7 K/9 rate across 14 starts. But the left-hander seemed to run out of gas in July, struggling to work deep into games before losing a permanent rotation spot when New York acquired Sonny Gray and Jaime Garcia. Likely to be better prepared to endure the rigors of a full season as a starter next year, Montgomery could become a lineup staple in 10-team leagues. 

Luke Weaver, starter, Cardinals
With reliable rotation members at a premium in today's game, sleeper starters such as Weaver will be wise choices in the late rounds of 2018 drafts. One of the most successful starters in the hitter-friendly Pacific Coast League during 2017, the 24-year-old has the skills to post helpful ratios and a high strikeout rate. Weaver isn't guaranteed to make the Cardinals' season-opening rotation in 2018, but he should get a chance to lock down a spot during Spring Training. 
Edwin Diaz, reliever, Mariners
Diaz was an early-season disappointment as he briefly lost his ninth-inning gig in 2017, but he showed improved form during the summer months. With swing-and-miss skills that compare favorably to those of nearly every reliever in baseball, the 23-year-old has the potential to join the top tier of fantasy stoppers by producing 40-plus saves and 100-plus strikeouts next season. 

Archie Bradley, reliever, D-backs
After struggling across 34 starts from 2015-16 (5.18 ERA, 1.57 WHIP), Bradley shifted to the bullpen this season and became one of the best relievers in the NL. The right-hander could soon take over the ninth-inning gig from 40-year-old Fernando Rodney and become an excellent fantasy closer in 2018.
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