For much of last season, the Diamondbacks’ rotation featured a pair of pitchers who delivered ace-caliber production and three others who turned in well above-average results, all of whom logged more than 150 innings. All five are back for this season.

The Diamondbacks’ bullpen, though not quite as impressive, wasn’t at all a weakness, and it returns several of the club’s better relievers from last year.

Lost amid the clamor for the Diamondbacks to re-sign slugger J.D. Martinez is the truth about who made the 2017 club a playoff contender. Here’s a hint: They were the ones who partook in the first official workout of spring training on Wednesday morning. And, no, it wasn’t the catchers.

“The narrative doesn’t change for me any year,” reliever Archie Bradley said. “Pitching wins. Every year you look at it, it doesn’t matter what hitters you have or how good your offense is. The playoffs show it every year. The guys that don’t give up runs are the teams that win. It comes down to pitching staffs.”

Said lefty Robbie Ray: “The hitting is always there. We’ve got guys up and down our lineup who can swing the bat. The biggest difference, I think, definitely was the pitching. Not only the rotation, but our bullpen was pretty solid, as well.”

Even the most cursory glance at the numbers last year’s staff compiled reveal the club’s dominance on the mound. A deeper dive makes the Diamondbacks’ accomplishments all the more impressive.

Both the rotation (third) and the bullpen (fifth) ranked in the top five in the majors in ERA. The staff as a whole was third with a 3.67 mark. The rotation’s 3.61 ERA was the lowest in club history.

Zack Greinke and Ray each received down-ballot Cy Young consideration, and Bradley tied for the highest WAR (wins above replacement) of any reliever in baseball.

The more advanced numbers show the Diamondbacks were historically good in the business of run prevention. Baseball-Reference has a statistic called ERA-plus, which takes a player or team’s ERA and adjusts it depending on park factors and league averages. It then converts it to a scale in which 100 is average and every point in either direction represents a percent above or below league average.

The Diamondbacks’ ERA-plus of 131 – i.e., the team was 31 percent better than the average pitching staff last year – was the seventh-best season since 1947. Last year’s Cleveland Indians staff are at the top of that list with a 138 ERA-plus, a number derived from their majors-best 3.30 ERA.

The Diamondbacks seem both aware of how well they pitched and confident they can do it again, as difficult as that might be.

For one, Ray and right-handers Taijuan Walker and Zack Godley each missed a handful of starts either due to injury or, in Godley’s case, because he began the year bouncing between the majors and the minors. Right-hander Shelby Miller threw well in four starts before succumbing to Tommy John surgery; he should be back by midseason. The team is hoping better health could mean even better results.

Another factor, General Manager Mike Hazen argues, is that, other than Greinke, the returning staff is filled with pitchers in their 20s, many of whom took big leaps forward. They say they’re still learning and could still yet improve.

“I just think with maturity, there’s probably a sharpness in execution and a consistency with the execution,” Hazen said. “Not asking them to be more talented, but asking them to hone in their consistency is an attainable goal as guys mature and get more experience under their belt.”

Plus, many of the peripheral explanations for the pitchers’ success remain in place this season. Two of the team’s three catchers return. The overall defense figures to remain strong. Pitching strategist Dan Haren, who spearheaded the daily game plans, is back, as are pitching coach Mike Butcher and bullpen coach Mike Fetters.

There’s also a new wrinkle being added to the equation: the use of a humidor at Chase Field, a climate-controlled chamber for baseballs that figures to make a significant impact on offensive production in the ballpark. 

The staff’s consistency was perhaps the biggest reason the Diamondbacks went from 69 wins in 2016 to 93 victories last year. And the ability to repeat that success figures to go a long way toward the team’s success this season – regardless of whether they find a way to sign Martinez.

Martinez, of course, would make any club better – the Diamondbacks included – and while his impact down the stretch last season was considerable, it likely didn’t make the difference between being contenders and also-rans.

The pitching, however?

“When you return five solid guys like that and the majority of your bullpen – you have to stay healthy and guys have to produce again, but, for me, it’s kind of like we’re ahead of the game,” Bradley said. “A lot of teams are searching for their fourth or fifth starter.

“Those guys, those starters, it’s not pressure, but they’re going to set the tone for us like they did last year. We’re going to follow their lead and they’re going to take us where we need to be.”

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Reach Piecoro at (602) 444-8680 or [email protected] Follow him on Twitter @nickpiecoro.