Top Candidates to Enjoy Breakout Seasons for Seattle Mariners in 2015

With a 6-3 win against the Colorado Rockies on Saturday, the Seattle Mariners wrapped up spring training and will now fly back to the Pacific Northwest for Opening Day.

Seattle's surprising decision to recall Carson Smith over Dominic Leone wrapped up the final 25-man roster. Minor league players also will get their assignments soon, with some of the Mariners' top prospects likely to head to Double-A or Triple-A.

Led by the likes of Felix Hernandez and Robinson Cano, these Mariners have the potential to make the postseason for the first time since 2001. But, Seattle will need a couple of breakout players rather than stars to elevate from wild card contenders to title threats.

A few breakout candidates, particularly Taijuan Walker and Mike Zunino, look ready to improve at the major league level. Others at various levels of the minors are primed for big seasons and could soon rise up prospect lists.

Taijuan Walker, SP

Spring stats rarely mean much in terms of predictive performance. Still, Walker's line jumps out with 25 innings pitched, one run allowed on nine hits and four walks with 24 strikeouts.

Even without looking at the stats, changes or new developments players make during the spring can be significant. Walker has shown some promising signs that he's ready to turn potential into production, both during the spring and his final start of 2014.

As Walker, 22, gets older and continues to develop, a slight uptick in velocity would be expected, and he has shown some of that this spring. Walker's fastball averaged nearly 96 mph in March, after sitting at 94.2 mph over his first 53 innings in the majors.

The pitch that looks most improved this spring is his changeup, which Walker was already developing nicely near the end of last season. He's throwing the pitch at 90 mph—a noticeable increase from a year ago, with superb location and deception. A 90 mph changeup with good downward movement may remind some Mariners fans of Hernandez.

Walker's curveball also is moving nicely this spring, and he has an already plus slider that also sits north of 90 mph on the radar gun.

Perhaps most importantly, Walker is on point with his command after struggling to throw strikes in his first stint in Seattle last year. All of the signs are there that he is ready to show more of that ace potential than ever before.

Mike Zunino, C

There isn't much that can be drawn from Zunino's 1.287 OPS in the spring, or the fact that his seven home runs rank second in the majors. Pitchers are working on things and not throwing their best breaking balls, which a hitter like Zunino is going to feast on.

However, there are some encouraging adjustments to take away from this spring. Zunino's plate discipline has been generally better during the spring, as he's posted a 14-7 ratio of strikeouts to walks in 58 plate appearances. He also has done a good job of avoiding the low and away breaking pitch that opponents killed him with in 2014.

That could be the result of swing adjustments Zunino attempted to implement during the offseason. Those changes include keeping the bat head in the zone longer and refining his approach with two strikes, which could help cut down on strikeouts and make Zunino drive the ball the other way more often.

Zunino believed that change in approach had an impact in spring training and will help him moving forward, via Shannon Drayer of 710 ESPN:

"

I feel like I am night-and-day better there. I feel like I know what I want to accomplish with two strikes. I feel like I have the base, and I can trust myself now instead of feeling like I'm going up there hoping to get a pitch to hit. That's the biggest thing, this feeling I am having now and I had in the early spring is something I am going to try to hold on whether it is video, whether it is mechanics. I mean, it's something I can go back to where I feel comfortable.

"

Given how quickly Zunino has risen through the various levels since being drafted in 2012, it makes sense that he has struggled with pitch recognition and making contact. With a full year of major league experience under his belt, Zunino should only get better in those areas.

Zunino has already proven he can more than handle the defensive, framing and staff-handling aspects of being a major league catcher. With a slight uptick in OBP, Zunino will be on the verge of stardom.

Ryan Yarbrough, SP

Ryan Yarbrough was a complete unknown when the Mariners selected him in the fourth round of the draft last season. It appeared as if Seattle was trying to free up some money to use elsewhere by signing a guy who was expected to go much later for way under slot.

Instead of fading into obscurity somewhere in Seattle's farm system, Yarbrough surprised by promptly striking everybody out in his first season of professional baseball. In 38.1 innings at Low-A Everett AquaSox, Yarbrough posted a strikeout rate of 36.6 percent.

Even more impressively, Yarbrough put up a minuscule walk rate of 2.8 percent. All of that led to a 1.40 ERA (1.88 FIP) with just one home run allowed.

The 23-year-old left-hander was first noticed by the Mariners for his excellent control and good use of a deceptive changeup. What makes Yarbrough really interesting is that his velocity keeps going up, as his fastball reached as high as 95 mph last summer after being more around 89 mph in college.

Yarbrough may have been viewed more as a reliever when drafted, but he's given himself a chance to be a starter down the road. He should move up into High-A or Double-A this year, and a similar performance will make him rise up prospect lists.

Edwin Diaz, SP

With Walker and James Paxton graduated to the majors, the Mariners don't have much top-end pitching depth left in their system. Diaz looks like the pitching prospect with the brightest major league future and is ready to establish himself as one of the top two or three overall players in the organization in 2015.

After debuting at just 18 years old in 2012, Diaz already has 204.1 minor league innings under his belt and is still at a young age for his level. Diaz ramped things up to 116.1 innings pitched as a 20-year-old at Class-A Clinton LumberKings last season, posting a 3.33 ERA (3.48 FIP) with a 23.0 percent strikeout rate.

As Diaz continues to develop and get a bit older, he has put some velocity on a fastball that now touches 96 mph and can be commanded well, at times. That's been aided by the fact that Diaz has put 20 pounds of muscle to move to 6'2" and 180 pounds, and he could use even a bit more weight.

MLB.com gave Diaz's slider a 55 grade last season, which has to be considered a plus pitch for his level. Developing a third pitch (he uses a very raw changeup right now) could determine how high Diaz's ceiling goes, but he's ready to turn some heads at more advanced levels of the minors.

All stats via FanGraphs.com, unless otherwise noted.