Biggest breakout prospect for each NL West team

Some prospects are highly touted heading into a season and then live up to advanced billing. Others are a bit more under the radar, either because they are coming off of injuries, haven't performed up to expectations or perhaps are just getting started on their pro careers. MLB Pipeline selected one of these type of prospects from each organization as a 2018 breakout candidate. We might not be talking much about the prospects below now, but they could jump on the scene in a big way this season.
• Impact prospects by division: NL East | NL Central | NL West | AL East | AL Central | AL West
Arizona: Mack Lemieux, LHP
Lemieux was drafted by the Nationals out of high school in 2015, then instead of heading to Florida Atlantic, he opted to go the junior college route. After a year at Palm Beach State, he was selected by the D-backs in the sixth round of the 2016 Draft and they were encouraged with his pro debut that summer. He struggled some during his first full season in the Class A Midwest League, partially because he didn't quite know what a long pro campaign looked like. It sounds like a lesson was learned because the 6-foot-3 right-hander came to camp this spring looking ready and raring to go.
"He came in better shape this year," D-backs farm director Mike Bell said. "He looks like he's in a better place than he was last year, which is normal, this being his second Spring Training."
Colorado: Colton Welker, 3B (No. 4 on Rockies Top 30)
Welker led Stoneman Douglas High (Parkland, Fla.) to the No. 1 national ranking in 2016 before signing with the Rockies for an over-slot $855,000 as a fourth-rounder that June. Multiple club officials have likened him to a young Nolan Arenado because they have similar builds and posted similar numbers in their first two pro seasons. Welker's batting average (.350), on-base percentage (.401) and OPS (.901) all would have led the low Class A South Atlantic League in 2017 if an abdominal strain hadn't sidelined him for two months and kept him short of the needed plate appearances to qualify.
Welker could post monster numbers in 2018 at high Class A Lancaster, perhaps the best hitting environment anywhere in the Minors. He has precocious feel for the barrel and pitch-recognition skills, allowing him to make repeated hard contact with ease, and he has the bat speed and leverage to produce 20-homer power once he gets stronger. A high school shortstop, he has solid arm strength and is making encouraging progress learning third base.
"The sky is the limit for Colton," Rockies farm director Zach Wilson said. "We love him a lot, his tools and his makeup. He never gets cheated on his swing and can hit for average and power. He's a good defender, with very good instincts, a great first step, natural fluid actions and a hose at third base. He works hard and his teammates love him."

Los Angeles: Mitchell White, RHP (No. 4 on Dodgers Top 30)
Walker Buehler surged from high Class A to Los Angeles in 2017, and the less-heralded White might have been right behind him if a broken toe hadn't sidelined him for two months. After having Tommy John surgery following his high school graduation in 2013, he burst onto the prospect scene as a redshirt sophomore at Santa Clara in 2016 and worked his way into the second round of the Draft. He limited opponents to a .172 average while striking out 88 in 73 2/3 innings and advancing to Double-A during his first full pro season.
When former Dodgers vice president of baseball operations (and current Braves GM) Alex Anthopoulos saw him last spring, he noted that White had stuff befitting a No. 1 overall choice. He can make hitters look bad with a variety of pitches: a 92-97 mph fastball with nasty sink and run, a power slider with late bite that he can turn into an equally effective cutter and a curveball that shows flashes of becoming a true hammer. If he can refine his changeup, control and command, he could be a frontline starter.
"White has an impact fastball," Dodgers farm director Brandon Gomes said. "He gets swings and misses at the top of the zone and something like a 70 percent ground-ball rate in the bottom half. He has a plus curveball and a plus slider, he's a competitor and he understands pitching. It's all there."

San Diego: Tirso Ornelas, OF (No. 15 on Padres Top 30)
A product of the Mexico Red City Devils team that netted the Padres Luis Urías and Andres Munoz, Ornelas landed a $1.5 million bonus from the Padres in 2016 as part of their massive international spending spree. He showed an intriguing blend of present skills and potential during his 2017 pro debut by slashing .276/.399/.408 with 17 extra-base hits and a 16.8 percent walk rate at age 17 in the Rookie-level Arizona League.
Listed at 6-foot-4, 180 pounds, Ornelas shows the makings of becoming an impact player with his size, athleticism and array of tools. He's an advanced hitter with a fluid but explosive left-handed swing that produces line-to-line contact and raw power. His patient approach, ability to recognize pitches and willingness to take walks all stand out for his age, and he opened eyes with his ability to handle center field during his pro debut.
"We've been very impressed with his athleticism," Padres farm directory Sam Geaney said. "He's ready to go to the [Class A] Midwest League. He's very physical and he's improved his athleticism since he signed. He's a very intriguing, exciting player for us."
San Francisco: Sandro Fabian, OF (No. 6 on Giants Top 30)
The receipient of the largest bonus ($500,000) in the Giants' 2014-15 international class, Fabian made an electric U.S. debut in 2016, batting .340/.364/.522 in the Rookie-level Arizona League. The Dominican made such an impression that San Francisco skipped him a level and sent him to low Class A last year. Despite an extremely aggressive approach, he was able to solve more experienced pitchers and batted .277/.297/.408 at age 19, including .352/.366/.535 during the final six weeks of the season.
Fabian has an uncanny feel for hitting, barreling balls with ease and showing the potential for at least average power. He also shows good defensive instincts as well, getting good jumps in right field and possessing a strong, accurate arm. His biggest need is to work deeper counts and not worry about hitting with two strikes after walking in just 3 percent of his plate appearances in his first three years as a pro.
"He improved as the course of the season went on," Giants assistant GM Jeremy Shelley said. "He had a strong second half and hit for power, though Augusta is a tough park. He has a chance to be a solid defender with a plus arm. As he gets better, he has a chance to be very good at the plate. Discipline is the key."