Will fantasy baseball difference-makers like Ryu and Devers keep it up?

Hyun-Jin Ryu has had a stellar fantasy baseball campaign, but will he keep it up the rest of the way? David Richard-USA TODAY Sports

Sure, Christian Yelich and Cody Bellinger may single-handedly be carrying many fantasy baseball managers' quest for a championship, but successful managers also probably found at least one gem outside of the top 100 draft picks.

I could've focused on so many other names but decided to do a deep dive on the five biggest middle-rounds difference-makers sitting closest to the top of my personalized ESPN Player Rater. Among those who missed the cut are DJ LeMahieu, Ketel Marte, Lucas Giolito, Shane Bieber and Mike Soroka. (If you have questions about those overachievers or anything else, drop me a tweet.)

What have these five players done to achieve these heights? More important for our purposes, can they sustain it?

Hyun-Jin Ryu, SP, Los Angeles Dodgers

Not even his recent stumble against the Boston Red Sox could push his ERA above 2.00. The fantasy community has known Ryu to be "near elite when healthy," and he's taken that to a higher level in this breakthrough campaign.

Though his 8.15 K/9 is actually at its worst point since 2016, he has altered several parts of his game which proves it's not a fluke.

A few key reasons: He's healthy for the first time in a few years, after enduring arm and shoulder issues. Ryu is also lobbing in a career-high rate of changeups (26.8%), which is helping him cope with this new homer-happy era.

The big move: The left-hander has also traded his slider for a cutter simply by changing the grip; he's modeled and studied CC Sabathia's, giving him a strikeout pitch to make up for his lower velocity and allow him to attack right-handed batters aggressively.

Opponents have limped to a .601 OPS against that pitch, which ranks Ryu fourth among those who've thrown it 300 times. This has played into his career-high ground ball percentage (51.9) and top-10 rank with an overall average exit velocity of 86.5 mph.

A problem that's struck many top pitchers this season has been a decline in results when runners are in scoring position, which has crippled their left-on-base rates. Ryu leads the majors with a 3.91 ERA with runners in scoring position, easily topping second-place Max Scherzer (6.44).

What now?

Though his suddenly elite ability to sequence against batters has me confident he can lead the league in that last category, I'm still a bit skeptical about how strong he'll finish there.

At this point in the fantasy season, Ryu can be trusted as a no-doubt ace, but to what level he wraps things up could make trading him a logical chess move. Perhaps a 3.50 ERA he could rationally post the rest of the way wouldn't be as helpful to your title hopes as a riskier top pitcher with more strikeout ability. And Ryu's injury history could always resurface unexpectedly.

Still, Ryu's cruise is far from a ride which you need to jump off; the Dodgers are in a great spot to help him finish with 20 wins, especially if they can improve their bullpen ahead of Kenley Jansen. Case-by-case situations aside, Ryu should use his newfound aggressiveness to rank among the top 15 or so starting pitchers, which should be good enough to ride out in most cases.

Rafael Devers, 3B, Boston Red Sox

Funny how many of us thought Devers was exposed in his second year, forgetting the hyped former prospect was just 21. Now that his .322 batting average ranks among the top five in the majors and his 17 homers put him on pace to easily clear his 21 from last year, it's easy to question the success.

But four notable improvements stand out for me. First, he's shined when he's made contact. Here's his progress from the past three years, per TruMedia:

His 2019 numbers rank third and second, respectively, in the majors.

Second: Devers is owning fastballs, posting a .969 OPS so far, topping his rookie-year .956 and outpacing last year's by 307 points. I'm a little worried that he's had a career-high pull rate (46.1 percent), which may lead to him losing some batting average if he goes through a slump.

However, for my third point, Devers has done a better job of keeping his hands through the strike zone to get ahead on pitches. This has helped him close the holes in his swings versus lefties, against whom he's batting .290/.317/.440, compared to .229/.272/.347 in 2018. Of course, a .409 wOBA versus righties would've erased any softness versus southpaws anyway.

Lastly, he's shown a more varied spray chart when leaving the yard. He's launched seven homers to center field, dwarfing the two he had in each of his first two seasons, and he's already matched his career high in 2017 of five opposite-field blasts.

What now?

He's tapping into what many were hoping he'd do when he was a prospect by fixing issues with his bat path. Those who call him a product of the new juiced-ball era are ignoring his development.

Given how much he's guiding pitches to right field, I wouldn't be surprised to see his batting average dip, and his average fly ball distance of 327.1 feet ranks tied for 83rd, so maybe he's getting a bit lucky.

Even with that risk, he should deliver enough power (10-plus homers) to counter any drop-off he may have there. Hitting mostly second in Boston's lineup has its perks, making him a candidate to lead the league in runs scored. That's a stat that easily helps someone stand out in fantasy scoring.

We're at a point in the season when it's more difficult to crater in batting average, but if that's a major concern, I'd understand if you flipped him in redraft leagues to avoid that outcome.

Charlie Morton, SP, Tampa Bay Rays

The veteran has kept Ryu from being the runaway profit winner among starting pitchers, adding a high-end strikeout performance (148) to his beaming ratios (2.35 ERA, 1.03 WHIP).

Morton is also top-10 in average exit velocity (86.6 mph), but his biggest boon has been the swings and misses he generates on his curveball: Uncle Charlie leads the majors with 106 swings and misses and 98 chases outside of the zone on his namesake pitch. He's not even afraid to throw it in hitters' wheelhouses, also topping MLB with 112 offerings in the zone.

That's helped cut his walk rate to a career-best 2.81 per nine. The righty has struck out fewer than six batters just three times in 20 starts.

What now?

Morton wisely chose to sign with a club that upholds pitching development as strongly -- arguably better, by many standards -- as his former club, the Astros, which helped facilitate his revival in 2017.

Of course, like Ryu, the 35-year-old has had trouble posting a full season in the past due to physical limitations. Perhaps Tampa Bay's suddenly crowded rotation, especially whenever Brendan McKay returns, will consider resting Morton for longer periods between starts so he can last through September and the postseason.

Those two fears of diminished volume may support the cause of his shareholders objectively shipping him away, but his skills will remain elite for as long as he steps on the rubber. If something close to his 3.62 ERA from 2017 is an acceptable floor for you the rest of the way, you shouldn't feel the need to sell -- especially since his favorable team context could push him toward 20 wins.

Josh Bell, 1B, Pittsburgh Pirates

After being critiqued for having erratic power for an up-and-coming first baseman, the 26-year-old has already topped his previous career high with 27 homers through his first 357 at-bats and is six RBIs away from matching his full-season best of 90 in 2017.

He hit 12 homers and 12 doubles in May, something only Hank Aaron and Frank Robinson did in a single month before him.

To help create the swing that vaulted him -- at least for this season -- into Hall of Fame territory, he did different offseason work and, as reported by the AP, was advised to carry a longer boom stick:

"[New Pirates hitting coaches Rick Eckstein and Jacob Cruz] worried hitting hundreds of balls off the tee each day would ingrain bad habits [in Bell], so they asked him to stop. They worried switching back and forth between bat lengths would disrupt his timing, so they suggested he take a 35-inch bat -- one of the few players in the majors able to handle a piece of lumber that size -- and stick with it."

At 6-foot-4, 235 pounds, Bell has seemingly benefited from the increased plate coverage, ranking fourth (tied) with a ridiculous 97.0 mph average exit velocity on four-seam fastballs; and seventh in average fly ball distance (349.2 feet).

What now?

PNC Park is surprisingly playing like a hitter's haven, so we can't make the "bad home park" argument anymore.

We can argue a few things may dip: The Pirates have had surprising production from its supporting cast (Bryan Reynolds, Kevin Newman), so perhaps Bell's teammates dropping off could put fewer runners on base for him. Bell also has endured a mini-slump by going 3-for-19 coming out of the All-Star break, and his strikeout rate is at a career-high 21.1%, so his batting average is trending downward to a more realistic level.

Still, even if he winds up hitting .270 at the end of the season, he'll keep afloat with his newfound power.

Luis Castillo, SP, Cincinnati Reds

When Castillo met his idol Pedro Martinez, he asked him about his changeup grip. The way the Reds hurler has deployed it in his young career, you'd think he simply snatched Martinez's body.

Castillo's 2.41 ERA ranks among the league leaders, and he has increased how often he's used his hitter-erasing string-pull to a career-high 32 percent.

I'd argue, however, that the underrated credit belongs to the weapon he's cultivated in 2019 to complement his top pitch: the sinker. His four-seamer has been "meh," but he's lowered his use of it in favor of the dipping, tailing heater, which has movement that resembles ... his changeup!

Castillo is exhibiting jaw-dropping talent that gives him one of the highest ceilings when building a fantasy staff in a dynasty league, even strong enough to wash away most of the concerns about his hitter-friendly home park. When I look deeper, though, I'm a bit less excited for the short term.

What now?

Here's where I'm a bit concerned about the near future: A starter's walk rate that hovers near Castillo's 4.50 rate this year can only work for so long to sustain an ERA this low.

Castillo still pitches from 1-0 a lot, posting a first-pitch strike on just 52.5 of plate appearances. In fact, he ranks last out of MLB's 80 qualified pitchers by throwing a pitch in the zone on 0-0 just 39.7 percent of the time.

Plus, Castillo has thrown his changeup in the zone just 32.5 percent of the time, ranking 23rd among pitchers who've used it at least 300 times. Sure, it's supposed to drop off the back to be effective, but if he has to keep battling from behind, hitters may eventually have better luck sitting back on the pitch.

To be fair, that type of backwards pitching could work with someone with his overpowering flair, and if you're chasing a fantasy title and crave strikeouts, you should feel hard-pressed to give him up unless overwhelmed in a deal.

But if you're stringently playing the ERA regression game in a single-year league, Castillo is an ideal sell.