The first time the D-backs lost Daniel Hudson to injury, it seemed like it would be a big blow to their playoff hopes, but Wade Miley stepped in and opened people’s eyes. When he went down the second time, it seemed like it would really put Arizona in a bind, as while Miley was by then a rotation fixture, Joe Saunders was out of action as well. Neither Josh Collmenter not touted prospect Trevor Bauer were able to get the job done, but the void has been filled quite amply as of late by left-hander Patrick Corbin.

Acquired by the Diamondbacks in the Dan Haren trade, Corbin was good enough that Marc Hulet ranked him as one of the D-backs top 10 prospects both this year and last, but wasn’t quite good enough to crack the top 100. He was ranked similarly this year by ESPN’s Keith Law. In other words, he was a sleeper.

Corbin first got the call to the Majors on April 30, when he replaced Collmenter, who had struggled to the tune of a 6.42 FIP in April. He didn’t exactly have a star turn, and he found himself back at Triple-A when Hudson returned from the disabled list just before Memorial Day. While it wasn’t a banner beginning for Corbin, there were positives. He kept his walks down, and he showed an ability to generate ground balls, as he netted 43 grounders versus 27 fly balls for a 1.59 GB/FB.

As he had done before his call-up, Corbin went back to Triple-A and pitched well. He was bumped back to the majors a second time at the end of June when Hudson hit the DL for the second and final time this season, but this time he worked in relief, shuttling between the roles of long man and lefty specialist. He handed both roles with aplomb, as he continued to generate more grounders than fly balls, kept his walk rate relatively low, and he added in a healthy dose of strike outs as well. The team sent him down again after the All-Star break when they needed a roster spot for Saunders’ return, but his stay in Reno would once again prove to be short-lived. When Arizona once again decided that Collmenter fit better in the bullpen — and he just may, as he has posted a 2.74 FIP in relief this season compared to a 5.14 FIP as a starter — Corbin was brought back for a third time, and was given another chance to start. He has run with that chance.

In his first three starts in this, his second iteration in the rotation, Corbin was tasked with taking on three playoff contenders. The first two were on the road against the Dodgers and Pirates. He pitched swimmingly in each, notching six-inning quality starts. But yesterday was a bigger test. The Nationals were in Phoenix, and came into yesterday’s game having won eight straight — including the previous two in Arizona, during which they had scored nine and six runs, respectively. Corbin held Washington to two runs over seven innings, saddling the Nats with their first loss in more than a week. That makes three quality starts and counting, a 19-inning span in which he has allowed just four runs.

Aside from the positive results against three playoff contenders, there are other positive takeaways here as well. First, Corbin’s velocity is up from earlier this season. In his first five starts of the season, his average four-seamer topped out at 90.5 mph, but in these past three starts, he has averaged at least 90.7 mph. The strikeouts have also remained, as Corbin has whiffed a batter per inning. And he’s doing so with an increased swinging strike percentage, giving rise to the notion that he has tweaked something for the better. It’s far too early to tell definitively, but the difference could be his slider, which has been much improved in these three outings. Looking at his season as a whole, another encouraging sign is his work against right-handed hitters, something that Hulet diagnosed as a potential problem for him entering the season. Holding righties to a 3.72 FIP while being death to lefties is a good recipe for success.

Corbin’s success these past three starts highlights the D-backs’ pitching depth. While many teams might have needed to trade for a starter to replace Hudson, Arizona was able to just reach down in its system. Bauer proved to not yet be ready the same way Wade Miley proved not to be ready last season, but Corbin was. That’s ridiculous depth. And if Bauer learns what he needs to in the minors and is ready to contribute next season the way Miley has this season, well then the D-backs will just go right on not missing Hudson. Arizona could open 2013 with a rotation of Ian Kennedy, Trevor Cahill, Miley, Corbin and either Bauer or Tyler Skaggs. This would allow them to let Saunders — who is actually having a nice season (for him) — walk, and use his $6 million elsewhere. It would also allow them to not rush back Hudson, and create competition in camp for the final spot(s) in the rotation as well.

No matter how general manager Kevin Towers and manager Kirk Gibson choose to fill out their rotation going forward, they will have a wealth of pitching at their disposal. The D-backs started the season with Hudson and Collmenter in the rotation, and may finish it with Miley and Corbin in their place. They didn’t need to make a trade to find two ample replacements, and they didn’t have to rely on their stud prospects Bauer and Skaggs. That incredible depth, most recently exemplified by Patrick Corbin, is going to make Arizona a contender for the foreseeable future. Corbin entered the season as a sleeper, but if he can maintain this level of effectiveness or something close to it, he won’t be slept on for much longer.