Seattle held a 2-1 lead to that point despite managing just two hits, both in the first inning, but couldn't hang on as the Yankees won two of three to improve their American League-best record to 59-39.
The Mariners finished with three hits on the day, falling to 43-57.
A hit batsman -- the fourth in two games by Seattle pitching -- ignited the Yankees' winning rally. Josh Kinney plunked Derek Jeter on the left hip with a fastball leading off the eighth. Robinson Cano and Mark Teixeira followed with singles off Lucas Luetge to load the bases before Luetge got Curtis Granderson to pop out to third baseman Kyle Seager in foul territory.
Manager Eric Wedge then brought on Kelley to face the right-handed-hitting Nix, who launched his bases-clearing double into left-center for a 4-2 lead. Russell Martin pushed another run across with a single before Kelley got Ichiro for the final out of the frame.
That at-bat figures to be Ichiro's last at Safeco this season, as he now heads to Yankee Stadium with his new team to open a weekend series with the Red Sox.
"I was here 11 1/2 years, and I didn't really show it, but inside I was going through some emotional times," Ichiro said. "It was very special these last few days."
Inserted into the leadoff spot by Yankees manager Joe Girardi for the series finale, Ichiro was greeted again by a standing ovation as he came to the plate in the first. Just as on Monday, in the first game after his trade was completed, the veteran outfielder stepped out of the box and bowed deeply to the crowd.
Ichiro grounded out in that at-bat and went 1-for-5 on the afternoon. After his fifth-inning single up the middle, he was thrown out trying to steal by catcher Jesus Montero, with countryman Munenori Kawasaki slapping his glove and yelling in delight after applying the hard tag as Ichiro slid into the shortstop's foot.
That caught stealing cost the Yankees a run, as Jeter followed with a single and Cano doubled to left, with Jeter holding at third. Both were stranded in scoring position when starter Hisashi Iwakuma got Teixeira to fly out to right for the third out.
Ichiro went 3-for-12 in the series with a double and one stolen base in two attempts and is batting .261 for the season. The crowd of 36,071 paid its dues to Ichiro, but the Mariners are prepared now to head in a new direction.
"We're moving forward," said Wedge. "I think it's another step now that these guys are leaving town. The focus for all these young kids is playing baseball and getting better and understanding what it takes to win a game like that today."
Iwakuma, making his fourth start since being moved into Seattle's rotation just before the All-Star break, went five innings and turned a 2-1 lead over to Oliver Perez. The right-hander allowed six hits with three walks and three strikeouts while throwing a season-high 95 pitches.
The former standout in Japan is now 0-1 with a 4.29 ERA as a starter with 14 strikeouts and 10 walks in 21 innings. Overall, he's 1-2 with a 4.56 ERA after pitching the first three months in long relief.
Iwakuma surrendered his lone run in the first, when Jeter homered to left-center on a full-count slider.
But the Mariners came back with two quick runs on starter Ivan Nova in the bottom of the first with Seager pushing the first across on a bases-loaded walk and Mike Carp following with an RBI fielder's-choice grounder.
Seager now has 60 RBIs in 100 games, just two shy of Miguel Olivo's team-leading 62 for the entire 2011 season.
The Mariners didn't get another hit until Casper Wells singled in the ninth.
"You're asking a lot of your pitching staff to hold those guys down for that many innings," Wedge said. "We almost squeezed by, but ultimately, you just can't play it that tight against a veteran offense like that. They really stepped up there in that eighth inning."
That didn't stop the Mariners from kicking themselves about blowing the lead. After giving up Nix's double, Kelley struck out Andruw Jones on a 97-mph fastball and clocked 95-96 on several other heaters.
The Safeco radar gun showed him at 98-99, but Kelley wasn't buying that.
"Maybe just out of pure anger," Kelley said. "I guarantee you it wasn't that [fast]. But today probably was the best I've felt, arm-wise. Sometimes the days you feel the best are the days you don't get it done, and sometimes you don't feel good and you do get it done.
"Sometimes you don't like this game when you leave the park. But I'll be back tomorrow."