NEW YORK -- There was plenty of warning as Isiah Kiner-Falefa prepared to make a relief appearance on Thursday, nudged to be ready to toss his second mop-up inning of the week. With the Yankees trailing by an eight-spot at the end of the third, the assignment hardly represented a surprise.

Once Kiner-Falefa tossed a perfect ninth inning, including his first career strikeout, he was caught off guard to learn that his workload was incomplete. His spot in the batting order was due up.

Thus, when Kiner-Falefa homered, it was officially as a pitcher -- the first Yankee to do so since the Nixon Administration, providing a moment of levity in an otherwise discouraging 10-2 loss to the Mariners at Yankee Stadium.

“Doing it twice in one week, I was just trying to go out there and have some fun,” Kiner-Falefa said. “I forgot about the at-bat. It came quick, and I just tried to get my swing off.”

Kiner-Falefa’s ninth-inning shot over the left-field wall sealed his place in Yankees trivia, making him the first Bomber to homer as a pitcher since Lindy McDaniel cleared the fences on Sept. 28, 1972, at Detroit. The American League adopted the designated hitter rule in 1973.

Nick Swisher was the most recent Yankee to homer and pitch in the same game, doing so on April 13, 2009, at Tampa Bay. Kiner-Falefa said that pitching is “not fun for me,” though he’s filled the role three times now, also seeing the mound on April 13 vs. Minnesota and June 16 at Boston.

“I want to be one of the best bench players in the league,” Kiner-Falefa said. “I’m taking pride in any opportunity I’m given. When I get those opportunities, I want to be ready, whether it’s pitching, hitting or defense.”

Wielding a fastball that averaged 76.2 mph, Kiner-Falefa moved from third base to the mound in the ninth inning. His services were needed because it was, as manager Aaron Boone put it, “An awful day at the park for us.”

Domingo Germán was hammered for the second consecutive start, permitting a career-high 10 runs (eight earned). Kolten Wong, Ty France, Teoscar Hernández and Cal Raleigh all homered off Germán, who completed just 3 1/3 innings.

“I thought stuff-wise, it was coming out hot, and then he just started making mistakes with his breaking ball,” Boone said. “Up in the zone, hanging it, spinning out a little bit and not having the command we’re used to seeing with Domingo, which is his calling card.”

Germán is just the third Yankee to allow 10 or more runs while surrendering four or more homers, joining Bob Turley (June 12, 1955, at Cleveland) and Whitey Ford (July 2, 1966, at Washington).

“Sometimes it happens,” Germán said through an interpreter. “It’s hard to figure out where the issue is; if it’s mechanical, the release point. Are they adjusting or seeing the pitch well? You’ve got to keep working. It doesn’t stop. You’ve got to find what kind of solution you can apply and put it to work.”

New York had few answers for Mariners right-hander Bryan Woo, who held the Yanks hitless until Gleyber Torres' one-out single in the bottom of the sixth.

“You’re in the arena and you get punched in the mouth, and it’s not fun to go through something like that, especially at home,” Boone said.

In his previous start, Germán allowed seven runs to the Red Sox at Fenway Park, a 15-5 drubbing that -- like Thursday’s contest -- was also a sloppy defensive exercise.

Among New York’s three errors, third baseman Josh Donaldson and Germán each committed miscues on a Mike Ford grounder in the third inning. Donaldson fumbled the ball, then threw to Germán attempting to cover third base, with the toss tipping Germán’s glove and bouncing into the dugout as a run scored.

“We had a chance to sweep today and we didn’t come close,” said Anthony Rizzo, who also failed to handle a ground ball in that inning. “Domingo was out there trying to give us some length and we’re booting balls behind him. That’s the really frustrating part of a lopsided game. We just want to play clean behind him.”