Patrick Corbin wasn’t Arizona manager Torey Lovullo’s first choice to start on Opening Day this year, or his second choice, or probably even his third. Among the Diamondbacks’ five main starters last season, Corbin finished with the worst ERA and peripheral numbers, and he was even worse the year before, posting a 5.15 ERA in his first full season back from Tommy John surgery. But a mid-March groin injury to Zack Greinke scrambled Arizona’s pitching plans, and because the rest of the rotation had already been spaced out to fill in after Greinke, Corbin was the best—though perhaps least enthralling—replacement option.

Or maybe Lovullo just knew in advance that Corbin would quickly blossom into one of the majors’ best starters. The 28-year-old southpaw beat the Rockies in his first start, struck out 12 Dodgers while allowing just one hit in his second, and pitched a complete-game one-hitter against the Giants in his fourth. Through six starts, Corbin’s stat line looks like that of a classic Randy Johnson Arizona campaign: He’s amassed a 4-0 record and 2.25 ERA while striking out 36.7 percent of hitters and walking just 4.7 percent.

Corbin’s breakout is even more meaningful in the context of Arizona’s spectacular start to the season. The Diamondbacks have won nine consecutive series to start the season despite facing a formidable set of opponents in that span, and after winning two of the first three games in a four-night set against the Dodgers this week, the Diamondbacks hold the majors’ second-best record and lead the NL West by five games, with an even greater eight-game lead over the five-time reigning division winners in L.A. They have a complete team with a new ace, a capable lineup, and a dependable bullpen, and they’re on a course to reach their first World Series since 2001—if the team’s growing list of torn ligaments and abdominal strains cooperates.

The disabled list has most worryingly claimed two members of Arizona’s rotation in the season’s first month. Last season, the Diamondbacks’ starters collectively posted one of the 10 best seasons of the wild-card era by ERA-, which adjusts ERA by ballpark and the league’s broader run-scoring environment. But Arizona benefitted from a fortunate dash of health in 2017: After a torn UCL befell Shelby Miller in April, the rotation remained healthy the rest of the way. The five main starters—Corbin, Greinke, Robbie Ray, Taijuan Walker, and Zack Godley, who was better than Miller after replacing him—all made at least 25 starts. Only one other team matched that level of durability from its entire rotation.

But Walker has already been lost for this year with a UCL tear of his own, and Ray is out for an unknown—and existentially fraught—duration after leaving his last start in the second inning with an oblique strain. Arizona entered the season with minimal rotation depth, and whatever internal contingency plans it had are already being stressed; general manager Mike Hazen said Tuesday that the Diamondbacks might resort to piggybacking two relievers in one starter spot or fiddling with a quasi-four-man rotation until Ray returns.

At least they have Corbin to stabilize the group with his newfound acehood. Baseball history is littered with players who took the league by storm in April only to fade over the course of a full season, but Corbin ranks third among qualifying starters in strikeout rate and second in strikeout-minus-walk rate, and it’s impossible to fake his level of dominance even in a small sample. FanGraphs has monthly splits going back to 2002, and in that span, 2018 Corbin ranks sixth in strikeout rate at the end of April (minimum 25 innings). The rest of the top 10 are new-look Gerrit Cole, Yu Darvish, Max Scherzer, Javier Vázquez, Chris Sale, Robbie Ray, Scherzer again, Noah Syndergaard, and José Fernández. That’s a list of uniformly elite strikeout pitchers, so either Corbin is a remarkable outlier or he’s improved by a remarkable amount.

The latter option seems more likely because, as The Ringer’s Ben Lindbergh wrote last month, Corbin has adopted the in-vogue strategy of throwing his best pitch more often, even if that pitch isn’t a fastball and therefore counters a century of baseball orthodoxy. It’s the Rich Hill plan, or the Lance McCullers model, and Corbin’s expanded and improved slider usage has transformed him into a Cy Young candidate and potential nine-figure free agent next winter. In Corbin’s career in the regular season, opposing batters have hit .157 and slugged .271 against his slider, compared to hitting .309 and slugging .497 against all other pitches; with that wide a disparity, it would be foolish not to throw his slider more.

The clearest illustration of Corbin’s evolution comes in the following graph, which shows how his slider and strikeout rate in two-strike counts have risen in tandem. He hasn’t been more successful at reaching two-strike counts this season, but he has more efficiently put batters away once he’s reached two strikes. In his career before 2018, he completed the strikeout in 45 percent of plate appearances that involved a two-strike count; this year, he’s up to 65 percent, which appears to be a direct result of wielding his slider more—and with more velocity—in a potential strikeout situation. No starting pitcher has thrown his slider more frequently with two strikes.

Corbin has been the beneficiary of a fair number of external factors in the early going, as well, which suggest he won’t retain such an extraordinary stat line over the full season. Only 10 qualified pitchers have allowed a lower batting average on balls in play, and only 10 have stranded a higher percentage of base runners. Both of those figures should regress somewhat to the mean going forward. Corbin has also exhibited a sizable home/road split (1.29 ERA at home versus 4.50 on the road, though his strikeout totals are sufficiently impressive in all locales), which don’t by themselves hint at anything untoward about his strong start, but are of note because Chase Field’s newly installed humidor appears to be working to dampen offense in Arizona’s home park.

The Diamondbacks’ home accoutrements aren’t the only factor that has afflicted Arizona’s offense this season, which makes the team’s start—it was tied for 11th in runs per contest through Tuesday’s games—all the more encouraging. Injuries have swept through the lineup, too, but that issue was more a short-term concern than what the rotation now faces.

Jake Lamb and Steven Souza, whom the team acquired over the winter as an ostensible J.D. Martinez replacement, are both on track for activation from the DL this month, which should bolster an imbalanced offense. They will help solve two of Arizona’s positional problems, as Baseball-Reference’s WAR values peg Arizona as below replacement level at third base and exactly replacement level at right field thus far. Lamb will displace overextended utilitymen Daniel Descalso and Deven Marrero at third base, and Souza will slot in as the everyday right fielder.

In the meantime, Arizona will hope for continued production from the lineup’s linchpins. Paul Goldschmidt’s strikeout rate is running well above his career norm (31.5 percent so far, versus a 22.1 percent career mark before this year), but his chase and whiff rates aren’t inordinately troubling, so it’s likely that his inflated total will adjust as the season progresses. And despite an early-season slump, Goldschmidt has already brought his season line back to his career level, as he’s already back among the top first basemen with his .255/.378/.472 slash line.

A recent power surge for A.J. Pollock, meanwhile, has given the Diamondbacks center fielder 10 home runs, which ties him for the league lead and already places him halfway to his career high. Pollock and fellow outfielder David Peralta (.300/.393/.520) likely won’t continue to hit at such prolific clips, but Lamb and Souza could compensate for any such ebbing.

The Diamondbacks’ bullpen rounds out a roster with few obvious holes, or at least ones that can’t be fixed with better injury luck. That group boasts a league-best 1.88 ERA, and while some of that success is a result of unsustainable batted-ball luck, Arizona still ranks fourth in reliever FIP and benefits from a collective capability. Lovullo’s pen has no weak links; of the nine relief pitchers he’s summoned this season, the highest relief ERA belongs to T.J. McFarland, at just 2.65.

A baseball team is a collection of individual parts, and all of Arizona’s components feature both top-level talent—from Corbin and Greinke in the rotation to Goldschmidt in the lineup to Archie Bradley in the pen—and a viable supporting cast. The foundation is less sturdy than that assessment implies, given the dearth of depth outside the 25-man roster, but Arizona has already built the largest division lead in the majors, and Monday’s announcement that Dodgers shortstop Corey Seager would miss the rest of the season due to his own UCL injury only widened Arizona’s margin for error against its most imposing division challenger.

And even before Seager’s injury, Baseball Prospectus thought so highly of Arizona’s roster and hot start that the PECOTA projection system gave the Diamondbacks the best odds of any National League team to win the World Series. Arizona made the playoffs last year but was quickly swept aside by the Dodgers in the division series, and few pundits considered the Diamondbacks likely to improve upon that showing this year.

But now they’re in first place, fueled by their dominance of the Dodgers and a new left-handed star whose statistics—if not physicality or demeanor on the mound—resemble quite closely the franchise’s last left-handed star, who happened to win a World Series Game 7. In Corbin’s most recent start, a Ryan Zimmerman line drive deflected off the pitcher’s bare hand, but after a visit from the trainer, Corbin stayed in the game. The injury scare epitomized Arizona’s greatest issue this season, but it also signaled at further dreams ahead: If the Diamondbacks maintain their early-season advantage, and if the health problems stop with Ray, the fifth starter–turned-reluctant–Opening Day–starter-turned–emphatic ace could use that hand this fall to pitch for a title.