Hernandez improved to 8-5 with a 2.82 ERA as Seattle won the series by taking three of four. The All-Star right-hander held the Royals to a run on eight hits and a walk before turning the game over to Lucas Luetge in the ninth.
"He pitched outstanding today," Royals manager Ned Yost said. "I don't know if the heat had anything to do with it, but he wasn't trying to blow hitters away. He was spotting his pitches really nice and commanded the ball as well as I've seen a pitcher command the ball all year long."
Rookie designated hitter Jesus Montero went 3-for-4 with a home run, double and four RBIs to lead the Mariners' resurgent offense. Seattle racked up 31 runs in the four games at Kauffman Stadium and has scored more runs on the road than any other American League team this season, while ranking last in home scoring.
The Mariners hit .325 with eight home runs and 20 extra-base hits in the four games.
"I thought it was a great series for us," manager Eric Wedge said. "I loved the way we played. It was a total team effort. When you talk about a vision of the way you want your team to play and go out there and play Major League baseball, this is about it. This is what we're looking for."
Montero went 10-for-17 in the series, improving his batting average from .242 to .262. After totaling just one RBI from June 1 to July 16, he's had eight in the past three games and 36 for the year.
"That means a lot to me," the 22-year-old Venezuelan said. "I helped the team to win. We scored six runs and four of those were mine. I'm swinging the bat well and seeing the ball well. I'm just trying to hit it hard and see what happens. Everything has been good."
The Mariners improved their road record to 23-27 (compared with 17-27 at home) as they head to Tampa for a three-game set.
Hernandez has been just fine wherever he's pitched over the past month as he's gone 4-0 with a 1.36 ERA (eight runs in 53 innings) with 59 strikeouts over his last seven starts.
The 26-year-old right-hander came into the game leading the Majors with 140 strikeouts and averaging a career-high 9.5 per nine innings but was more of a ground-ball machine in this one.
"His off-speed stuff is so deadly that you just can't get behind in the count, so our goal was attack him early," Royals first baseman Eric Hosmer said. "It's why he's one of the best pitchers in the game. He was pitching to the situation more.
"There were a couple times with guys on base where he got big ground balls. That's the thing with great pitchers. They just don't go for the strikeouts, they play the situation."
Hernandez gave up a pair of singles in each of the first two innings but escaped both times with the aid of double-play grounders. From there, he limited the Royals to just a run in the fifth on an RBI single by Chris Getz that ended his scoreless streak at 19 2/3 innings.
By that time, the Mariners had scored four runs on rookie left-hander Will Smith. Three of those came in a four-hit second inning that included a leadoff home run to straight center by Montero.
The 413-foot blast was Montero's ninth long ball of the season but first since June 16. Michael Saunders then drove in a run with a single to right and Brendan Ryan followed with a sacrifice fly for a 3-0 lead.
Montero added another RBI in the fifth with a single to left after Ichiro Suzuki had doubled and moved to third on a wild pitch, then did it again with a run-scoring double in the seventh for a 5-1 lead. Montero knocked in his fourth run on a sacrifice fly in the ninth.
Hernandez dug deep in the eighth after loading the bases with one out, striking out Alcides Escobar and getting Billy Butler on a groundout to escape the jam.
Though he'd thrown just 89 pitches, Wedge then made the call to the bullpen.
"As hard as he'd worked and hot as it was, I didn't want him to have to go out and work hard in the ninth and have it affect his next start," Wedge said. "I know it was 89 pitches, but he threw 24 in the eighth and I felt that was enough."