This ability -- honed, guided and recently rewarded in the form of one of baseball's richest pitcher contracts -- allows Hernandez to take a 5-2 record and a sparkling 1.53 ERA into Tuesday night's start in the Bronx vs. the Yankees, even as the Mariners' bats continue their uphill climb into relevance and even as his average fastball velocity is a shadow of what it once was.
"Unpredictability is the word," pitching coach Carl Willis said. "You can't really look for one pitch against him. He's definitely special. The way he competes and the way he enjoys competing, you don't see it very often."
What we don't see anymore -- at all -- is the 100-mph heat that Hernandez had at his disposal when he was a 19-year-old rookie. The rate of decline in his velocity over the years since is either alarming or awe-inspiring, depending on your perspective.
On the alarming side, you note these average fastball velocities dating back to Hernandez's age-21 season in 2007 (courtesy of FanGraphs.com) and worry that they are a sign of an elbow due to give out from wear and tear:
Age 21: 95.6
27 (this season): 91.1
Hernandez is an "old" 27, if that makes any sense, because he's already thrown 1,679 innings at the Major League level. That's why there was all that hand-wringing over his medicals at the time Seattle signed him to a seven-year, $175 million contract in February. (The Mariners received a conditional $1 million option on Hernandez for 2020 if he is on the disabled list for more than 130 days in any season -- or consecutively over two seasons -- at any point in the deal.) And certainly, concern over anybody who does something this physically unconventional this long, this often, is justifiable.
The awe, however, comes from the fact that despite the velocity dip, Hernandez has maintained relatively stable ground-ball and fly-ball rates since 2008 and a strikeout percentage of at least 20.4 each year of his career. And this season, that strikeout percentage is 25.3 through eight starts, a career best.
As his fastball lost its zip, Hernandez adapted, becoming a much more polished, in-control arm. His walk rate declined from 9.3 percent in '08 all the way down to six percent last year. This season, Hernandez is letting just 3.6 percent of plate appearances against him get to ball four.
Dare I say it: Felix Hernandez has never been better than he is right now.
"Listen, velocity is great," Willis said. "I think it's a big part of why you see strikeouts increasing, with the power arms, particularly coming out of the bullpen. But regardless of the velocity, the key to it is being able to change speeds off of whatever that top velocity or that average fastball is. That's what Felix does. He pitches. I think he's a better pitcher now than before."
Hernandez takes pride in the thought.
"It's true, it's true," he said. "It's definitely true. Before, I had two pitches only -- just a fastball and a curveball. Now, I try to hit the corners with my breaking ball and changeup."
Hernandez is getting more swings outside the strike zone than ever before in his career. The opposition is batting just .213 with a .576 OPS against him.
Alas, the Mariners' batters still aren't faring much better on those days when Hernandez takes the hill. Dating back to 2008, Seattle has averaged just 3.79 runs of support for Hernandez in his starts -- the lowest such number among all qualifying starters in the Major Leagues in that span. That number is at 3.38 this season.
It is that lack of support that kept Hernandez from reaching the 100-win threshold until this year. But he's never complained about the impact on his own legacy, and he never demonstrated anything but a desire to be a "Mariner for life" before the February deal made that a possibility.
"He's a great teammate," manager Eric Wedge said. "I think he shows it the most if he does have a tough loss or maybe we don't play particularly well behind him. That's when he shows his leadership value and just how great a teammate he is. That's the greatest testament to Felix Hernandez, to me. It's not just the good days, but the tough days as well."
Hernandez had what was, for him, a tough day last week, giving up a first-inning run and knowing, instantly, that his pitches weren't as crisp as he'd like them to be. He went eight innings anyway. Eight mostly-dominant innings that built upon what is looking to be another sensational season.
"If you don't have your best stuff," Hernandez said afterward, "you've got to go out there and fight."
And few put up a better fight than King Felix.