In his last three starts -- three Seattle losses -- the 2010 Cy Young Award winner has allowed 14 earned runs and 24 hits. Hernandez is 1-4 with a 6.37 ERA over his past six starts, including a loss to the Padres in his last outing after a 10-day layoff to rest a sore back.
"I'm tired of pitching like this," Hernandez said after his most recent start. "I've got to do something about this. I've got to pitch better."
And the Mariners, who snapped a six-game slide with a 7-4 win over the Giants on Saturday, are in desperate need of production from their ace.
Hernandez worked on reducing his body turn on his windup this week, citing that he noticed he'd changed his approach slightly over the past months.
"Just having something to focus on can make a big difference," manager Eric Wedge said. "Something to help get you back in line or something that allows you to feel better about what you're going to do."
Wedge said Hernandez was throwing the ball well in his start against the Padres and that one rough inning -- a four-run sixth -- tainted what was otherwise a solid outing.
"I think he should build off his stuff and the way the ball was coming out of his hand and the life he had at home plate," Wedge said. "Hopefully he can really use that and work off that. Now he's going to be getting more consistent work. I'd like to see him get into a rhythm."
Madison Bumgarner will take the mound for the Giants. In his last start, the 22-year-old southpaw limited the Astros to just one run in 7 2/3 innings.
But that was in San Francisco, where Bumgarner has experienced most of his success.
The left-hander, who boasts an 8-4 mark and 3.08 ERA, has been dominant at home, but has been less effective on the road. He is 5-1 with a 2.27 ERA in six starts at AT&T Park, but is 3-3 with a 3.89 ERA in seven starts on the road.
Mariners: Gutierrez gets some rest
Center fielder Franklin Gutierrez will be back in the lineup Sunday after getting most of Saturday off.
Gutierrez was activated off the disabled list and rejoined the Mariners on Wednesday after recovering from a torn pectoral muscle suffered early in Spring Training.
Wedge said he plans on giving Gutierrez regular off-days after he missed a substantial amount of time. Gutierrez went 1-for-2 Saturday after entering the game as a pinch-hitter in the sixth and staying in as the designated hitter.
"We're going to ease him in here for the first 10 days or so and pick some spots for him," Wedge said. "He played two days in a row and with the day game [Sunday], this was a good time to get him a little break and get him back in there tomorrow."
Giants: Lincecum on losing skid
Felix Hernandez isn't the only struggling West Coast ace.
Tim Lincecum allowed five runs in Saturday's loss to the Mariners. Over his last eight outings, Lincecum has surrendered at least four earned runs seven times and has lasted seven innings only twice.
Lincecum hasn't recorded a win since April 28 against the Padres. Since then, Lincecum is 0-5, and the Giants are 0-9 in his nine starts.
Kevin Millwood allowed nine hits in five innings Saturday, his first start since leaving June 8's combined no-hitter with a slight groin pull after six innings.
Dustin Ackley had two hits Saturday night. He has hit safely in eight of his last nine games.