It took a walk-off single by Justin Smoak in the bottom of the ninth to win this one, a welcome breakthrough for the Mariners first baseman and a team that struggled to score runs throughout a 3-6 homestand.
But the biggest development figured to be the return of the King after he'd gone 1-4 with a 6.37 ERA over his previous six starts.
"Felix is Felix," said Smoak, still cleaning a shaving-cream pie out of his hair following the postgame celebration. "When he doesn't dominate, everybody freaks out. But he's going to dominate. That's what he does."
The biggest challenge now for Hernandez might be equaling the gift-giving bar set by his wife, Sandra, and their two youngsters, Mia and Abraham.
"That was amazing. That was the best gift ever," Hernandez said. "I told the guys, 'I've got to step it up now. I've got to do something good.'"
Hernandez supplied his teammates with a welcome chance to pull out a second straight victory over the Giants, which they did when Smoak drove home pinch-runner Munenori Kawasaki from second with the winning run on a one-out single off reliever Javier Lopez.
Kyle Seager and Jesus Montero led off the ninth with singles against reliever Sergio Romo. Chone Figgins, pinch-running for Seager, was thrown out at third on a sacrifice attempt before Smoak delivered the first walk-off hit of his career.
For his efforts, Smoak got the shaving-cream pie treatment from teammate John Jaso during a postgame TV interview.
"That might have been the fastest I moved all day," said Smoak, who also robbed Hector Sanchez of a potential go-ahead single in the eighth with a diving stop at first.
Mariners closer Tom Wilhelmsen got the victory after maneuvering out of a one-out, bases-loaded jam in the top of the ninth.
Wilhelmsen hadn't allowed a run in 10 2/3 innings over his previous eight outings, but gave up a single and two walks to load the bases before striking out Melky Cabrera and getting pinch-hitter Nate Schierholtz to ground a 3-2 pitch to second base.
"That was big," said manager Eric Wedge. "You're going to go through everything when you pitch in that ninth inning. How you handle it more than likely will dictate whether you're going to stay there or not. And he handled it in a very strong fashion today."
The big out was getting Cabrera, who is hitting .360 on the season.
"The guy he was facing had pretty electric stuff," said Giants starter Madison Bumgarner. "The odds are always in the pitcher's favor, obviously. But we had the guy we wanted up there. That's one of the few times he didn't come through for us."
Hernandez gave up just one run on six hits with one walk and seven strikeouts, turning a 1-1 tie over to his bullpen in the eighth after throwing 113 pitches. With the no-decision, he remains 4-5 with a 3.52 ERA.
Hernandez has been struggling for the past month, and Sunday didn't start much differently. He needed 30 pitches to get through the first inning, though he allowed just one run in escaping a bases-loaded situation after three singles and a walk.
But from there, the Mariners ace returned to King-ly form and held the Giants scoreless over his final six frames, to the delight of those in attendance on Father's Day.
The Giants advanced only one runner past first in Hernandez's final six innings, that coming when Buster Posey was given second base on a third-inning balk. The Giants tried to sacrifice a runner in the seventh after a leadoff single, but catcher Miguel Olivo made an excellent play on the bunt to throw out Brandon Crawford at second.
The Mariners didn't make much headway against Bumgarner, either, totaling just three hits and one walk through eight innings against the 22-year-old lefty. They had runners on first and second with one out in the eighth, but Bumgarner got Ichiro Suzuki on a tapper back to the mound and struck out Franklin Gutierrez.
Seattle had tied the game at 1 on a sacrifice fly by Dustin Ackley in the second as Casper Wells slid around the tag attempt by Sanchez at home. Wells had led off with a single and moved to third on Olivo's double.
"Great slide," said Wedge. "That looked like an old-school hook slide there. It was good to see. We did some of the little things you need to do to win those type of ballgames. Casper has played well since he's come back."
Wells went 1-for-3 on the day and is 6-for-12 in his first four games since being recalled from Triple-A Tacoma on Wednesday.