Hernandez more than held up his end of the bargain, going seven innings, giving up two runs on five hits and striking out six batters to up his American League-leading total to 153. He departed with a 3-2 lead that grew to 5-2 when Kyle Seager's two-run single in the bottom of the seventh provided a comfier cushion.
X-rays on Hernandez's left hand were negative, and despite the fact that he got a no-decision, all signals moving forward were positive for the right-hander.
"I felt strong today, but a little wild, too," Hernandez said. "I fell behind a couple of times. When I got in trouble, I made good pitches and got out of the innings."
But relievers Lucas Luetge, Brandon League and Oliver Perez combined to give up three runs in the top of the eighth, the tying blow coming on a two-out, two-run single by Eric Hosmer.
Fortunately for the Mariners, first baseman Mike Carp is back from the disabled list and getting hot. Carp, who went 3-for-4, doubled to lead off the bottom of the eighth. Pinch-runner Munenori Kawasaki scored when Trayvon Robinson's sacrifice bunt was fielded by pitcher Jose Mijares, who promptly threw the ball over Hosmer's head at first base, allowing the go-ahead run.
Casper Wells added what proved to be the decisive run off Greg Holland that made it 7-5.
"Any time they score, you definitely want to work the comeback right away," Seager said. "You don't want to let a little momentum go. We've done a good job this series of scoring early and then trying to match them when they score."
The result put a happy face on what could have been a bummer for Hernandez, who was gunning for his 10th victory of the season, although for a brief moment in the fourth inning, it looked like he might have to go on the disabled list.
Hernandez was hit in the meaty part of the left hand by a Hosmer line drive, and the right-hander yelled, stomped around the mound, and displayed a noticeable wince on that famous face of the Seattle franchise.
But he shrugged it off and went back to work, throwing 101 pitches in his seven innings and hitting 94 mph on the radar gun in his last frame of work. He lowered his season ERA to 2.79.
"We didn't get much off Felix all day and to get back there in the eighth inning and tie it was a pretty big boost for us," Royals designated hitter Billy Butler said. "We just couldn't hold on to it."
The Mariners got RBI doubles in the second inning by Carp and the fourth inning by Robinson, and Brendan Ryan added a sacrifice fly in the two-run fourth off Royals left-hander Will Smith to build the 3-2 lead.
Hernandez wasn't overly dominant, scattering five hits and giving up a run in the fifth inning after a Chris Getz single and a Jarrod Dyson walk led to an Alcides Escobar RBI fielder's choice, but he was in control.
So was closer Tom Wilhelmsen, who gave up a run but held on for his 14th save of the season.
Now the Mariners take a four-game winning streak and a bit of mojo into Monday's series opener against Toronto.
"That was a fight, and you knew it was going to be today," Mariners manager Eric Wedge said. "Last game of the series, young team over there is not just going to go away, and they didn't go away.
"Both teams fought very hard, both teams had to come back, but these are the type of games where you're glad you're the home team. You get those final at-bats when you need them."