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The Diamondbacks rotation rocked in April, but can it continue?

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The Diamondbacks started off the season red hot but lost Shelby Miller. A look at the rest of their overachieving rotation.

MLB: Cleveland Indians at Arizona Diamondbacks Mark J. Rebilas-USA TODAY Sports

The Arizona Diamondbacks currently lead the majors in starting pitcher fWAR. Over the course of 28 games, they have set the pace with the Rockies atop the National League West. While the Giants are sputtering (and have to go without their ace for at least a few months), the DBacks’ rotation has been second to none.

Shelby Miller prematurely left a start on April 24th, and over the weekend Arizona announced the forearm injury was indeed the precursor to season-ending Tommy John surgery. Although Miller had hardly been exceptional in his handful of starts this year, he pitched well enough to keep the Diamondbacks in games.

Zack Greinke has to live with a decrease in his velocity, something he struggled with last year when he was basically a league-average pitcher. In just six starts this season, Greinke has posted nearly half the value he did last year (0.9 fWAR compared to a 2016 total of 2.2). This season, Greinke’s xFIP and FIP are identical at 3.24, and his ERA is in line with those numbers at 3.19. More importantly, he has increased his strikeout rate and decreased his walk rate. Though this is a good thing, you have to wonder if it’s sustainable. At the age of 33, is he really going to post his best strikeout rate in six seasons?

Greinke is allowing significant contact as well, with a soft-hit rate at only 18 percent. Nearly 82 percent of all opposing contact is categorized as medium-hit or hard-hit. It’s hard to figure out why Greinke’s strand rate is a full 10 points higher than his career average when most contact is well-hit. It’s no surprise that his 91 cFIP is identical to last season. All in all, Greinke is likely the pitcher he was last year, as opposed to a reinvention of his old self.

It’s been a long time coming for a Taijuan Walker breakout, and so far, he is outpacing his previous success. Over nearly 30 innings this season, he has posted a career-high 26.4 percent strikeout rate, and career-low 5.6 percent walk rate. His last start was the real gem of the season so far, when he went eight strong innings, striking out 11 Padres and walking zero. Unlike Greinke, Walker’s current 90 cFIP is much improved from last season's 102. It also helps that he had 10 bone spurs removed from his foot in the offseason (ouch!).

Despite Patrick Corbin’s lack of power stuff, he keeps the ball in the park, and has allowed hard-contact on only about a quarter of batted balls. Like Greinke, though, Corbin’s 100 cFIP projects him in the future to be more like his 2016 self than his 2015 self. His 5.16 DRA belies his shiny 2.29 ERA. Don’t expect it to continue.

At 25 years of age, Robbie Ray is probably the most interesting of this group. Ray’s 3.0-fWAR 2016 campaign and career high 174 innings pitched put him on track for a 200 inning 3-5 Win season. This season, his ERA and xFIP place his numbers around 20 percent better than league average, confirmed with a 91 cFIP and 66.7 DRA-. Ray’s biggest issue this season has been his walk rate, which to date, has been significantly higher than previous seasons. Interestingly, opposing hitters seem to be laying off his pitches at better than average rates. Batters have offered at only 57.4 percent of pitches in the zone, compared to league average of nearly 64 percent. He could see an uptick in strikeouts from all those called strikes.

Even though he’s not an ace, the loss of Shelby Miller makes things that much more difficult for the Diamondbacks. Greinke’s excellent start is more likely than not a one-month sample of overachieving with limited stuff. Walker continues to get better, but he’s unlikely to reach ace status for the remainder of this year. Corbin’s performance is not likely to remain much (if any) above average, and Ray, though young and solid, still has progress to make.

The Diamondbacks have an average to slightly above average rotation, with upside potential from Robbie Ray and Taijuan Walker. They have put themselves in position to be relevant well into the summer, especially since other wild card contenders are suffering serious rotational problems (the Giants with Bumgarner and the Mets with Noah Syndergaard).

This rotation is not likely to bring the DBacks to the World Series, but they had a strong enough April where they can stay relevant for a good portion of the season. Unfortunately, if Greinke and Corbin regress, they could be out of the playoff hunt as quickly as they came into it.

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Steven Martano is an Editor at Beyond the Box Score, a Contributing Prospect Writer for the Colorado Rockies at Purple Row, and a contributing writer for The Hardball Times. You can follow him on Twitter at @SMartano