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Listen, nobody really knew how Masahiro Tanaka was going to fare against MLB hitters upon his arrival from Japan. The New York Yankees made a $175 million leap of faith in his ability to perform well, but it was just that: a leap of faith.

One month in, we can say this: Well played, Yankees.

Tanaka hasn't just fared well against MLB hitters. He's dominated them. What's more, the signs are there that he's not about to slow down.

The 25-year-old right-hander made his final April start Sunday night against the Los Angeles Angels at Yankee Stadium. It had some icky parts, as Tanaka walked four, hit a batter and gave up a home run in six and one-third inning. Given that he began the night with a four-start streak of at least seven innings pitched, no HBPs and only two walks, you might say it's the worst we've seen of Tanaka.

But then there's the part where he struck out a career-high 11 and only gave up two earned runs, helping to lead the Bombers to a 3-2 victory. To these ends, it was yet another dominant start.

That makes five dominant starts, and Tanaka's overall numbers are certainly of the eye-popping variety. In 35.2 innings, he's struck out 46, walked only six and compiled a 2.27 ERA.

It's the strikeouts and walks that catch your eye, as well they should. As ESPN Stats & Info and Baseball-Reference.com can vouch, that's historic numbers:

Knowing this, it's hardly surprising that the beginning of Tanaka's career is the most promising we've seen among Japanese rookie pitchers who made at least four April starts.

Courtesy of a list from Baseball-Reference.com, here are some telling statistics from FanGraphs:

Debut Aprils for Japanese Pitchers Player Year GS IP K/BB ERA FIP xFIP SIERA Masahiro Tanaka 2014 5 35.2 7.67 2.27 2.92 2.06 2.08 Yu Darvish 2012 5 33.0 1.94 2.18 3.31 3.98 4.13 Koji Uehara 2009 5 30.0 3.17 4.50 4.60 4.93 5.00 Kenshin Kawakami 2009 4 21.2 1.64 7.06 6.24 4.69 4.59 Hiroki Kuroda 2008 5 30.2 2.00 3.82 4.24 4.52 4.71 Daisuke Matsuzaka 2007 5 33.0 3.80 4.36 2.91 3.41 3.21 Kei Igawa 2007 4 26.2 1.46 6.08 6.05 5.64 5.19 Kazuhisa Ishii 2002 5 29.2 2.13 3.03 2.83 3.60 3.65 Masato Yoshii 1998 4 25.0 2.38 2.16 3.62 NA NA FanGraphs

Note: I didn't include Hideo Nomo in the conversation because his debut month happened in May. But for those wondering, he posted a 1.96 K/BB, a 3.82 ERA and a 4.07 FIP.

If you're in the dark on what FIP, xFIP and SIERA are, those are fancy-pants metrics designed to calculate what a pitcher's ERA should be by focusing on things he can control.

FIP and xFIP do that by focusing on strikeouts, walks, HBPs and home runs, with the difference between the two being that xFIP replaces a pitcher's home run total with an estimate for how many homers should be on his record. SIERA's more complicated, but it's best known as the metric that actually tries to evaluate balls in play rather than ignore them.

What these three metrics tell us is that Tanaka's 2.27 ERA is one that he actually deserves based on how he's pitched. That's a feather in his cap because:

The same can't be said of the other sub-3.00 ERA guys above: Masato Yoshii and Yu Darvish . FIP , xFIP and SIERA have been known to be more indicative of a pitcher's true talent than ERA.

Which means that, yeah, the dominant Tanaka we've seen in April is no illusion. He's a legitimately dangerous match for major league hitters.

He should continue to be so as long as he keeps up the things that have made him successful.

Unless you're R.A. Dickey, it all starts with the fastball. You might remember that was a point of concern as Tanaka was circling a move to the majors, as the word on his heat was that it might be too straight to cut it in the majors.

Ben Badler of Baseball America, for example, wrote this last August: "Even though Tanaka can reach the mid-90s, his fastball is the pitch that gives some scouts pause because it comes in on a flat plane, making it more hittable than the velocity might suggest."

It's a good thing, then, that Tanaka hasn't relied too heavily on a straight fastball. According to Brooks Baseball, he's thrown a two-seam fastball about as often (22.9 percent) as he's thrown a four-seam fastball (24.1).

And despite the .333 average against said two-seamer, Tanaka being willing to feature it hasn't been for naught. It has a 53.9 GB/BIP (ground balls per balls in play) rate, helping his overall GB% climb to 48.2 (see FanGraphs).

The one thing that wasn't a concern was Tanaka's command. He had done no worse than a 1.4 BB/9 in any of his last three seasons in Japan, and the scouting reports tended to agree his command really was that good.

Thus far as a major leaguer, Tanaka has yet to give any excuses for that part of the scouting reports to be rewritten. Even after his four walks Sunday night, he still only has a 1.51 BB/9 for the season. He also owns an overall strike percentage of 68.7.

Matt York

According to Baseball-Reference.com, only three starters in the last two seasons have proven capable of posting a strike percentage that high and a walk percentage that low: David Price, Bartolo Colon and Cliff Lee.

Pretty good company right there, but none of the three is capable of getting as many swinging strikes as Tanaka.

Through his first five starts, Tanaka has a swinging-strike percentage of 11.8. That's way above the MLB average for starters of 8.7 percent.

How Tanaka does it is becoming less and less of a secret: He has a slider that right-handed batters can't lay off or hit, and he has a splitter that neither righties nor lefties can lay off or hit.

Here, behold some drool-worthy data from Brooks Baseball:

Masahiro Tanaka's Slider and Splitter Pitch Type Split Freq Swing% Whiff/Swing% K Slider RHB 28.63 50.67 47.37 10 Splitter RHB 18.32 62.50 63.33 14 Splitter LHB 30.24 68.00 54.90 13 Brooks Baseball

We heard that Tanaka's secondary stuff was good, but these numbers serve to highlight how they've managed to surpass expectations. They've been better than good. Hell, they've been great.

There's a good explanation for that. As reported by Brendan Kuty of NJ.com, Tanaka said in March that the bigger, slicker balls used by MLB gives his breaking stuff "more bite compared to balls in Japan."

Tanaka's splitter, in particular, has been downright devastating, and Katie Sharp tells us that hitters aren't getting any closer to unlocking the secret to hitting it:

Simply laying off Tanaka's splitter would be one solution, but the old "easier said than done" saying applies there.

Both righties and lefties have made that clear by swinging at over 60 percent of the splitters Tanaka's offered, and it's hard to blame them. His splitter breaks late and it breaks hard, and he's proven to be a master of locating it where hitters will have no choice but to chase.

Which is another thing about Tanaka: The rate at which he's getting major league hitters to chase pitches out of the strike zone is frankly absurd.

Tanaka entered his start Sunday with a O-Swing% (the percentage of pitches batters swing at outside the strike zone) of 43.2. Since the data first started being tracked in 2002, the highest O-Swing% for any pitcher with at least 150 innings stands at 37.2 (Cole Hamels last year). Getting hitters to chase at over 40 percent of pitches outside the zone just isn't something that pitchers do.

Are you getting the point that this guy's legit yet?

I hope so. It would be one thing if all Tanaka had going for him through five starts was a low ERA, but he has a heck of a lot more than that.

He has metrics that say his talent is for real. He's adjusted his fastball usage to help keep the ball on the ground. Best of all, he has a pile of strikeouts and a significantly smaller pile of walks that he's arranged by way of very good command and secondary offerings that nobody can hit.

There's still plenty of season left, and Tanaka has six more years on his contract after this one. If you're waiting for the lows, don't worry. Just because we haven't seen them yet doesn't mean they're not coming.

But make no mistake: Judging from what Tanaka has shown so far, there ought to be a heck of a lot more highs than lows in his future.

Note: Stats courtesy of Baseball-Reference.com unless otherwise noted/linked.

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