Mariners manager John McLaren said Hernandez "deserved better than that. He pitched really well. That's probably the best stuff he had all year."
Hernandez (2-5), whose start was pushed back two days because of a sore right calf, had allowed just one run and two hits before the eighth.
Dustin Pedroia broke the tie with a two-out RBI ground-rule double to left. After David Ortiz was intentionally walked, Manny Ramirez stroked an RBI single to right. Mike Lowell's infield single just wide of third scored Ortiz, and the final run scored on Jason Varitek's bases-loaded walk.
"It was pretty good in the first seven. The eighth, too, pretty good. It was bad luck," Hernandez said. "We have struggled so much right now.
"Everything was good tonight -- everything. That was a two-seamer to Pedroia that came back too much. Right in the middle of the plate, and he hit it pretty good."
The Mariners, who just came off an 0-6 road trip, needed a strong start from Hernandez. They got it, but couldn't finish it.
"I'm not frustrated," the young righty said. "I just have to find a way to win some games. That's all."
Both starters were efficient early. Bartolo Colon (2-0) retired seven straight before Kenji Johjima's one-out, third-inning double into the left-field corner. Yuniesky Betancourt followed with a single to right, too hard to score Johjima. Ichiro hit a too-shallow flyout to center. Then Jose Lopez grounded out to second baseman Julio Lugo, who made a diving stop.
Hernandez set down the first 11 in order, moving his fastball around and freezing the hitters with his breaking ball. But Ortiz, selecting a low changeup, crushed his 12th home run, a two-out shot in the fourth to dead-center.
Boston threatened in the fifth, beginning with J.D. Drew's one-out single to right. Varitek followed with a first-pitch line shot over Ichiro's head in center. But Ichiro stayed on it, finally catching up and hauling it down over his right shoulder.
Just as he caught it, he slammed hard into the center-field wall and bounced to the ground. During impact, Ichiro transferred the ball to his throwing hand as he was falling and still managed to flip the ball back to the infield.
"That was a great catch. That was as good a catch as I've seen Ichiro have," McLaren said. "That was fabulous."
The play carried more than just a little emotion for Ichiro. He said that "people" felt he should have made the catch Sunday on Jose Molina's game-winning double that allowed the Yankees to win, 6-5.
"That really ticked me off," Ichiro said through an interpreter. "So today, I thought to myself, 'I'm going to go for this ball, no matter what. I don't care if I get injured or anything.' I had a lot of stress piled up from [Sunday]. That was my thought.
"I don't remember much. I just let my body go. I kind of thought the wall was near, but I don't remember much in my mind."
Ichiro remained on the ground for a few minutes, but stayed in the game. When he returned to the dugout, he was given a standing ovation.
"That was a great catch," Hernandez said. "The defense was unbelievable. Those guys go out there and do the best they can."
In the sixth, Ichiro sparked a rally. He singled to right and moved to second when Lopez was hit by a pitch. Jose Vidro advanced the runners with a sacrifice bunt. Then Raul Ibanez finished an eight-pitch at-bat with a right-side groundout, scoring Ichiro.
Beltre also made a dazzling ninth-inning play to keep the deficit at four runs. With the runners on first and second and no outs, he made a dive to his right to stop a Pedroia ground ball. He crawled on his knees to tag third base, then got up and made an off-balance throw to first to complete a double play.
"We've picked up our defense quite a bit here lately," McLaren said. "We're still having a little problem with runners on third base and less than two outs. We have to get those guys in."
The Mariners were 2-for-9 with runners in scoring position. They were 9-for-44 over their previous four games.
The Mariners added a couple of runs in the ninth on an Ichiro RBI single and a wild pitch.
"There's some encouragement," McLaren said. "We're just looking for a win. Moral victories are not what we're looking for."