Hernandez was 1-9 with a 5.54 ERA in 13 post-August starts over the last three seasons, but he started this September with a gem against the rival A's in a game he called "special," given the growing importance of each contest as the Mariners push for their first playoff appearance since 2001.
"It means a lot," Hernandez said. "We came here to win the series, and that's what we did. Going against Lester, I knew it was going to be tough. I just had to make good pitches."
Seattle closed the gap to 3 1/2 games behind second-place Oakland in the AL West as the A's have gone 7-16 since Aug. 10.
"We're obviously looking up at them right now," said Seager. "We know where we are, we know they're ahead of us. So to come here and take two of three is big."
And who better to have on the mound in a big game than Hernandez, as the 28-year-old remains the clear leader for the AL Cy Young Award with a 14-5 record and 2.18 ERA, having bounced back from a three-game winless stretch.
Manager Lloyd McClendon has juggled his rotation recently to give all his pitchers extra rest, and he said Wednesday's game was evidence of why that strategy was important.
"He had tremendous command, he was down in the zone, he was 94 [mph] when he wanted to be 94, he elevated when he wanted to elevate," McClendon said. "He made one bad pitch on a swing-back fastball that ran back over the plate just a little too much. But he was vintage Felix today.
"It's a grind for all pitchers this time of year. I know we were doing the right thing by giving him and the other guys extra days. One of our pitchers couldn't even toe the rubber. I know we're doing the right thing. Today speaks volumes for that."
After giving up just six home runs in his first 24 starts this season, Hernandez has allowed eight in his last five outings, including a solo shot by Adam Dunn in the fourth inning that staked the A's to a 1-0 lead. But that was the lone blemish, and Hernandez said it was his only bad pitch of the day.
"He was really good," said Dunn, who hit his second homer of the series after being acquired from the White Sox on Sunday. "I've never seen him bad. Doesn't happen very often. We just didn't have very many opportunities today."
Dunn has 22 homers on the year and 462 in his career, 34th on baseball's all-time list. But Hernandez continued climbing his own ladder as he hiked his season totals to 206 innings pitched with 209 strikeouts, becoming the first Mariners pitcher with six 200-inning and 200-strikeout seasons in a career. Randy Johnson had five during his time with Seattle.
Hernandez has a 19-7 record and 2.58 ERA in 34 career starts against the A's, including 4-0 with a 2.15 ERA in five starts this season.
With the Mariners trailing, 1-0, into the seventh, Seager drove a 3-1 pitch into the right-field seats for his career-high-tying 22nd homer. Hart, playing his first game since being recalled from a rehab stint for a bruised knee on Monday, followed with a solo blast of his own to left field for a 2-1 lead on his sixth home run.
Seager went 3-for-4 with a home run and a double as five of Seattle's seven hits off Lester went for extra bases, though he limited the damage to just two runs in his eight innings.
"That one felt good," Seager said of his long ball. "He's such a tough at-bat. He's obviously one of the best pitchers going. In that situation, where you haven't had a lot of opportunities, you get in a hitter's count and just try to be aggressive. Fortunately for me, I was able to put a good swing on it."
Hart said he took heart from Seager's success and wasted no time following with the game-winner on an 0-1 fastball.
"That was huge," he said of Seager's bolt. "Lester is their best guy and one of the better guys in the league. It's always tough to score. After they got ahead, we just tried to find a way to get going. Seager has been a stud all year, so once he tied it up, I just was trying to make contact and get something going for the rest of the guys. And I was able to get something in the air."
Fernando Rodney closed out the ninth with his 41st save of the season, putting him four shy of Kazuhiro Sasaki's club-record 45 set in 2001.
"I feel like this is the playoffs right now," said Rodney. "That's what I want. That's the feeling right now. We have to keep playing a really aggressive nine innings every game and see what happens."