Originally written on The Outside Corner  |  Last updated 11/18/14

The debut of a top young prospect is becoming a weekly occurrence in MLB. On Tuesday, pitcher Zack Wheeler made his first major league start for the New York Mets. The 23-year-old threw six shutout innings, holding the Atlanta Braves to four hits in a 6-1 victory. Wheeler struck out seven batters while walking five.  Last week, the Pittsburgh Pirates' Gerrit Cole introduced himself to the big leagues. He earned a win in his first appearance, allowing two runs and seven hits over 6.1 innings versus the San Francisco Giants.  Those two debuts follow the grand entrance of Los Angeles Dodgers outfielder Yasiel Puig. The Cuban slugger has been a sensation in his first 15 games, providing the Dodgers with some excitement in what's been a disappointing season. Through 60 plate appearances, he has a .474 batting average and 1.289 OPS. Puig hit his fifth homer of the year in a 6-0 win over the New York Yankees on Wednesday.  It's too early to put this trio in the running for National League Rookie of the Year. But if those three players continue a high level of performance, they'll join what is already a strong race for the award with several future stars making an impact this season. Though it's only mid-June, who look like the top contenders for Rookie of the Year honors thus far? Two candidates have probably emerged as the favorites, yet at least a couple of others are making a strong case for themselves as the season progresses.  Evan Gattis, Atlanta Braves: Gattis emerged as the early favorite for the award, slugging six home runs with 16 RBI in April and easing any worries the Braves may have had about catcher Brian McCann beginning the season on the disabled list.  The 26-year-old followed up April with an even more impressive May, batting .317 for the month with a 1.065 OPS, along with another six homers and 16 RBI. How's that for consistency? He currently has a .252 average and .852 OPS, leading all MLB rookies with 14 homers and 37 RBI. Gattis's story is also tremendously compelling. The media has fallen in love with the journey of a kid who gave up baseball and bounced around the country working odd jobs and battling depression as he tried to find his purpose in life But Gattis has struggled in June, likely due to less playing time and no regular spot in the lineup with McCann's return. Going on the disabled list with a strained oblique could ultimately hurt his chances for NL Rookie of the Year if the injury lingers and keeps him sidelined for a longer period.  Shelby Miller, St. Louis Cardinals: Even without Gattis' injury, Miller may have already established himself as the leading contender for top rookie honors.  With Chris Carpenter likely to miss the season as he continues to work his way back from thoracic outlet surgery, the Cardinals needed someone to take his spot in the rotation. Jaime Garcia's shoulder surgery further exacerbated that need. Fortunately for St. Louis, the organization already had one of the best pitching prospects in baseball ready to contribute. In 14 starts, Miller has compiled an 8-4 record and 2.08 ERA. The 22-year-old right-hander also has 96 strikeouts in 86.1 innings, averaging out to 10 Ks per nine frames. Among Cardinals starting pitchers, Miller has the highest strikeout rate and allowed the fewest hits (6.7) per nine innings. Jake Westbrook has a lower ERA, but has made only eight starts.  As a rookie, the Cards will eventually probably have to limit Miller's innings later in the year or give him a rest at several points during the season. Until that happens, however, he's been a major factor in St. Louis emerging as the best team in MLB. Jedd Gyorko, San Diego Padres: Gyorko doesn't get as much attention as Gattis and Miller, playing on the West Coast and for the Padres. But the 24-year-old infielder has emerged as one of San Diego's most consistent hitters during the first half of the season.  Gyorko won a starting job out of spring training, solving the Padres' problem at second base. But he also helped out by filling in at third base when Chase Headley began the season on the DL. Only four MLB rookies have played at least 60 games thus far and Gyorko has the best numbers among them. He's batting .284 with an .802 OPS, 17 doubles, eight home runs and 25 RBI. His 20 walks and .341 on-base percentage lead all major league rookies as well.  Suffering a groin injury that put him on the DL could hurt Gyorko's shot at NL Rookie of the Year. It's also a major blow for a Padres team that is surprisingly competitive in the NL West. If San Diego eventually falls out of contention, Gyorko will surely earn less consideration than those rookies contributing to playoff races.  Julio Teheran, Atlanta Braves: The fifth spot in the Braves' starting rotation was a question mark coming into the season. But Teheran's development has settled such concerns.  The rookie got off to a rough start, compiling a 5.08 ERA in April while allowing 39 hits and eight walks in 28.1 innings. Since then, however, he's been one of Atlanta's best starting pitchers. In eight starts during May and June, Teheran has gone 4-3 with a 2.50 ERA. He's also struck out 46 batters and walked eight in 54.2 innings during that span.  Overall, the 22-year-old has a 5-3 record and 3.36 ERA in 13 appearances. Teheran also took a no-hitter into the eighth inning on June 5 against the Pittsburgh Pirates. He allowed one hit over eight innings with 11 strikeouts and two walks.  Teheran will be overshadowed by Miller among NL rookie pitchers and by Gattis on his own team. But if he continues pitching well for a playoff contender, he could finish among the top three vote-getters in NL Rookie of the Year voting.  Didi Gregorius, Arizona Diamondbacks: Getting a shortstop of the future was an offseason priority for D-Backs general manager Kevin Towers. Towers finally got one in a three-team deal with the Cincinnati Reds and Cleveland Indians. But there was some question as to whether or not Gregorious could hit well enough to be an everyday major league shortstop. Last year, the 23-year-old infielder hit .265 with a .717 OPS between Double-A Pensacola and Triple-A Louisville.  But Gregorius got off to a hot start with Triple-A Reno this season, batting .387 with a 1.069 OPS, albeit in only 33 plate appearances. That apparently gave Arizona enough confidence to call their shortstop up when Aaron Hill went on the DL with a broken hand. Gregorius quickly settled any concerns about his ability to hit in the majors. In his first 30 plate appearances, he batted .407 with a 1.226 OPS. Obviously, he wasn't going to maintain that pace and manager Kirk Gibson has had to move Gregorius down in the batting order as he's struggled. But a .289 average and .792 OPS with four home runs and 15 RBI is production that the D-Backs welcome at shortstop.

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