Maybe he had a little illicit help.
The rookie left-hander from Japan allowed three soft hits in 7 2/3 innings. After the game, Yankees manager Aaron Boone said he was aware that cameras showed a dark substance -- perhaps illegal pine tar -- smudged under the brim of Kikuchi's cap.
"I heard they were talking about it, so I was made aware of it sometime, like, in the eighth inning there," Boone said. "So I'll take a look at it, and we'll kind of see what we can make of it."
A team spokesman for the Mariners said Kikuchi would not comment about whatever was on his hat.
Although it's against the rules for pitchers to put any foreign substance on the ball, word is that many of them use pine tar or some other sticky material on their fingers to help with their grip.
It's one of baseball's worst-kept secrets. But pitchers are usually pretty discreet about it, and plenty of hitters would rather face a pitcher with reliable control than one who might let slip a 95 mph fastball sailing toward their neck.
Still, pitchers have been punished in the past for putting pine tar on the ball. Former Yankees right-hander Michael Pineda was ejected and suspended after getting caught in Boston.
Healy homered and hit three doubles to help the Mariners win for only the second time in 10 games. Mitch Haniger and Edwin Encarnacion went deep as Seattle (20-19), which opened 13-2 this year, snapped a seven-game losing streak at Yankee Stadium and avoided dropping below .500 for the first time since the final day of the 2017 season.
"This is the place where all the history of baseball is the center point," Kikuchi said through an interpreter. "I was really excited to go up there, and it was amazing."
After walking his first batter, Kikuchi (2-1) retired 16 in a row before Mike Tauchman fisted a bloop double over third base with one out in the sixth for New York's first hit. DJ LeMahieu followed with a single, and Luke Voit's sacrifice fly prevented a shutout.
"He was executing pitches, locating them and spotting them as good as you can," Yankees designated hitter Miguel Andujar said through an interpreter.
Facing an injury-depleted New York lineup stacked with eight right-handed hitters, Kikuchi was in complete control in his second consecutive stellar outing. Featuring an effective slider and curve, he struck out three and walked one while throwing 74 strikes on 106 pitches, his most in nine major league starts.
"He pitched really well and really shut us down," Boone said. "He was in command from the get-go."
In the offseason, the 27-year-old Kikuchi signed a four-year, $56 million contract with Seattle that could be worth up to $109 million over seven seasons if options are exercised.
Last time out, he allowed only one run and three hits at Cleveland, striking out 10 in seven innings.
"Yusei was awesome. He just kind of took over the game," Mariners manager Scott Servais said. "He's continuing to get more comfortable, understand who he is. He really looks forward to coming into Yankee Stadium and places he's thought about since he's a little kid and getting an opportunity to pitch there. He's taken it and run with it, so really a big boost for us tonight."
Encarnacion hit a sacrifice fly in the first and a solo shot off Jonathan Loaisiga (1-1) in the fifth. It was Encarnacion's second homer in two nights, fourth in five games and 12th of the season.
Healy hit a two-run shot in the eighth to help Seattle score five times in the final two innings. He finished 4-for-5.
Loaisiga was recalled from the minors to start in place of the injured James Paxton, acquired from Seattle in an offseason trade. A year ago on this date, Paxton pitched a no-hitter for the Mariners in his native Canada against the Toronto Blue Jays.
Mariners: SS Tim Beckham was rested. ... The team expects 3B Kyle Seager (left hand) will be ready to come off the 60-day injured list when he's eligible on May 25. Seager could begin a minor league rehab assignment in the next five or six days. ... Servais said his guess is live batting practice will probably be the next step for LHP Wade LeBlanc (strained right oblique).
Yankees: C Gary Sanchez and OF Brett Gardner were rested. ... There's a chance CF Aaron Hicks (lower back strain) will be reinstated from the injured list this weekend when New York plays at first-place Tampa Bay, Boone said. Otherwise, it could be on the following home stand next week. Hicks, sidelined all season, played nine innings in center field and went 0-for-3 with a walk on Wednesday in his third rehab game for Class A Tampa. He is hitless in 11 at-bats and scheduled for a day off Thursday. ... 3B Gio Urshela fouled a ball off the bottom of his left knee in the seventh and was removed after the inning. X-rays were negative, and Urshela has a bruise.
Healy has 16 doubles, one more than his total last season in 133 games.
After the game, the Yankees optioned RHP Jake Barrett to Triple-A Scranton/Wilkes-Barre.
Mariners: RHP Mike Leake (2-3, 4.91 ERA) pitches Thursday in the finale of a four-game series. He lost both his previous starts against the Yankees but hasn't faced them since 2014 with Cincinnati.
Yankees: After a rough start to the season, LHP J.A. Happ (1-3, 4.93) has a 3.12 ERA in his past four outings. He is 4-2 with a 5.06 ERA in seven career starts against the Mariners, who traded him to Pittsburgh in July 2015.
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