Twenty-seven up, 27 down. Again.

Seattle’s Felix Hernandez threw Major League Baseball’s third perfect game of the season Wednesday — a record — joining San Francisco’s Matt Cain and the White Sox’s Philip Humber, who also tossed his gem at Safeco Field.

That means six of the 23 perfectos in baseball history have come since 2009. Little wonder this is being called the Decade of the Pitcher.

Still not impressed? It gets better. Hernandez’s gem was the sixth no-hitter this season. One more and major league pitchers will have tied the seven set in 1990 and matched a season later.

There’s only been one year with eight no-hitters. Want to guess? Here’s a hint: Chester Arthur was president.

That season was 1884.

Let’s look at six reasons why pitchers have become so dominant:

TALENT ON THE MOUND

Headlines these days are more likely going to be made by a Jered Weaver or Johan Santana than a slugger, and rightly so. Pitchers are getting the best of the matchups again.

Starting with 1995, the heart of the Steroids Era, the best three years for earned-run average are 2010-2012 — it’s 4.21 this year, third best, according to STATS LLC. Led by hard-throwing Justin Verlander and knuckleballer R.A. Dickey, hurlers have a strikeouts/9 innings ratio over seven (7.09) for the first time since ’95, STATS says.

PLAYER DEVELOPMENT

Pitch limits. Cut fastballs. Better training techniques. The trend over the past decade has been to spend on building farm systems and developing pitchers from the draft — and then protecting those assets.

The Mariners have rejected all offers for the 26-year-old Hernandez when their team has needs in all areas. The Washington Nationals are first in the NL East with a rotation topped by homegrown stars Stephen Strasburg and Jordan Zimmermann.

The Giants shelled out big money to retain Cain in early April. Raise your own star rather than pay big bucks for a free agent and a team earns some cost certainty, too. It takes six years of major league service to reach free-agent status.

FIELDING

The newest of the new baseball metrics focus on the defense. Thanks to comprehensive video recording systems at the ballparks, computers are churning out complex spray charts and helping track batter tendencies with precision.

Seattle General Manager Jack Zduriencik is a big proponent of runs saved by defense and maybe that helps explain why two of the Mariners’ three no-hitters in club history have come this season.

HITTING

Home runs are down. Runs are down. The fact is hitters often look overmatched these days. Opponents’ batting average has not been this low since 1995, according to STATS. Pitchers are holding batters to a .260 average this year. In 2010 and ’11 it was .261.

LUCK

No, we’re not talking about players taking a seat far away from a pitcher with a no-no in progress. That’s superstition.

We mean the call that goes a pitcher’s way — i.e. Carlos Beltran’s ball ruled foul but TV replays showed it clearly landed on the left-field line in Santana’s no-hitter. Or that impossible-seeming play: Cain got two.

Mike Baxter made a bone-jarring catch to preserve Santana’s no-hitter in June, slamming into the wall during a play that landed him on the disabled list. Everyone can use a little luck now and then.

DRUGS

The suspension of Melky Cabrera on Wednesday shows the system is working. The gaudy numbers of the Steroids Era are gone, and while hitters weren’t the only ones cheating, pitchers appear to be getting more benefit from a return to a level playing field.

With big boppers not nearly as readily available these days, emphasis has shifted away from the long ball — except in New York — and pitchers have reasserted themselves at the top of the game.