The Cardinals are on pace to have the single greatest earned run prevention season of the last 100 years. There's plenty of qualifiers to that and reasons why it's not likely to keep up over the course of the entire year, but over the first three months, that's a cold hard fact. They're preventing runs in a way no one alive has ever really seen before -- and they're doing it without ace Adam Wainwright, who injured his Achilles tendon in just his fourth start of the season.

We'll get to how they're doing it, but first, let's explain how we can make that exclamatory statement. In order to compare across seasons and eras, we're using a relatively simple metric called "ERA-," read as "ERA minus," which sets league-average as 100. If you're familiar with OPS+ or ERA+, it's the exact same principle, except that excellent ERA marks are supposed to be lower, not higher. The Cardinals have a 69 ERA-, which means they're preventing earned runs 31 percent better than league average, a mark not topped since the 1909 Cubs of Three-Finger Brown and Orval Overall.

So, how are they making this happen? Perhaps the most interesting thing about the St. Louis pitching is that at first glance, they seem more "good" than "great." Their team strikeout percentage is tied with the White Sox for seventh. Their team walk rate is tied for fifth with three other teams. They're good at inducing grounders (47.3 percent) but not world-beaters at it (tied for fourth with the Giants). Even looking at Statcast™ exit velocity allowed, the pattern continues -- 87.85 mph is above-average, yet only eighth overall. While they're very good at preventing homers (second to the Pirates), so far nothing shouts "historically notable."

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Instead, they've been absolutely dominant at exactly the right times, which is to say, the big run-scoring hit that brings in three just never seems to come. Just look at the difference in their performance when men are on base as compared to with the bases empty:

Bases empty: .261/.313/.390, .309 wOBA (16th overall.)

Men on base: .204/.279/.300, .255 wOBA (1st. By a lot.)

With no one on, the Cards are essentially an average pitching staff, similar to the Yankees and Reds. With men on base, they become a shutdown team to an absurd degree, with a 27-point (in wOBA) gap between them and the No. 2 team, Tampa Bay. To put it another way, opposing hitters go from being Brandon Phillips against them with no one on to being Billy Hamilton with men on base.

A perfect example is in the performance of Michael Wacha, who starts against Andrew Cashner and the Padres on MLB Network's Statcast™ Showcase on Thursday night. Wacha's peripherals haven't been terribly different than they were in 2014. He's striking out slightly fewer than he did last year, but he's making up for it by walking fewer, and he's allowing the same rate of homers. His 3.14 FIP, unsurprisingly, is all but identical to last year's 3.17.

But that ERA has dropped from 3.20 to 2.77, and like his teammates, it's because of high-leverage success. With the bases empty, he's allowed a very good .282 wOBA. With men on, that's just .254. In part, that's because when there are runners in scoring position and two strikes, he increases usage of his sneaky-good changeup, his best whiff pitch. In those situations, the change usage jumps 12 percent, and it's an effective pitch in part because he throws his fastball so hard that he can get away with throwing his change so hard. Only Stephen Strasburg, Felix Hernandez, and Carlos Carrasco get higher perceived velocity on their changes -- for Wacha, the 7.07 foot extension on his change is second only to CC Sabathia for the pitch -- and that's fine company to be in.

With the exception of the underrated Lance Lynn, who has earned every bit of that 2.74 ERA, it's like this up and down the staff, with ERA marks that outshine peripherals. Unfortunately for the Cardinals, that disconnect is why this particular level of historical excellence is probably not sustainable all season long. Last year, they were worse with runners on base than empty. Of course, considering what they've done so far, they don't need to keep it up. Even a step back is still outstanding, and the playoffs seem all but guaranteed.