BOSTON — Sonny Gray was a prized commodity at last year’s trade deadline, ultimately landing in the Yankees’ rotation at a cost of three valued prospects sent to the Oakland Athletics.

On Thursday, Gray was demoted to the bullpen hours before a critical four-game series against the AL East-leading Red Sox.

It was a decision the right-hander could scarcely debate.

“They’ve given me ample opportunities to turn it around,” said Gray, whose awful 2.2 innings Wednesday against the lowly Orioles ballooned his ERA to 5.56 and sealed his fate.

“I’ll go down there and hope to turn things around,” said Gray, vowing to be ready to contribute in a long relief role.

“You get to this point of the season, it’s about winning games,” Gray said. “The best thing for this team will be to go down there.”

Newly acquired right-hander Lance Lynn will take Gray’s spot, beginning on Monday at Chicago against the White Sox — another club bound for a 100-loss season.

Gray will be available out of the bullpen on Saturday, though manager Aaron Boone floated the idea that “we very well may need him back in the starting rotation very soon.”

Veteran lefty J.A. Happ landed on the 10-day disabled list Thursday due to hand, foot and mouth disease, though the club is hopeful he’ll miss just Saturday’s scheduled start.

There’s an opportunity for Gray to be used as a sixth starter during this stretch of games without an off day until Aug. 20, but “I think it’s the best for everyone involved right now,” Boone said of Gray’s role change.

Lynn’s scoreless 4.1 innings in relief of Gray might have cemented the notion that the Yanks had a ready alternative.

The right-handed Lynn has a 4.89 ERA this year, but he’d pitched better of late in Minnesota’s rotation, prompting the Yankees — after acquiring Happ from Toronto — to send first baseman Tyler Austin and minor league pitcher to the Twins for Lynn.

Boone made the rotation decision in concert with pitching coach Larry Rothschild on Wednesday night and informed both parties on Thursday afternoon.

Still, Boone pitched the relief role to Gray as “a really important one” on a club that stood 5 1/2 games behind the Red Sox entering Thursday.

“Maybe it gives him a break from the grind, a little timeout,” Boone said of Gray finding “something” in the bullpen he couldn’t in 21 starts this year.

But inconsistent command of his fastball-curveball arsenal, the inability to finish hitters with two strikes and the snowballing effect of rough innings — leading to short starts — put Gray in this position.

“I’m going to come in with a positive attitude … with a smile on my face,” said Gray, an interesting choice of words based on the negative fan reaction of his nervous grin upon Wednesday’s short exit. “And (I’ll) do whatever I can to help the team win.”

Despite the epic struggles at Yankee Stadium, Gray doesn’t believe it’s a case of New York being too big of a stage.

“I think that I’ve struggled on the field. I don’t know how else to say it,” said Gray, who has a 7.71 ERA in 11 home starts this season, as opposed to 3.62 on the road. “The type of competitor I am, (I know) I can pitch anywhere.”

Gray hopes that being in the bullpen can help “simplify” his approach.

“It’s really hard to struggle here,” Gray said. But as the song goes, if you can overcome that and make it in New York, “you can go anywhere.”

At times on Thursday, speaking in the middle of Fenway Park’s cramped visiting clubhouse, Gray hesitated as he searched for the right words.

“It’s been a long 24 hours,” said Gray, including a Twitter controversy, when an indelicate tweet from his past came to light. “But, I think everyone knows who I am and what I’m about,” Gray said. “Even today … I’ve had a lot of support within this own clubhouse, outside of this clubhouse — wherever.

“I think you learn kind of what … drives this, how ridiculous it can be sometimes. It’s been rough, but I’ve had a ton of support.”

Boone offered that Gray is “really close to being a very good starting pitcher,” citing the stuff and the track record and his age.

At 28, Gray is still controlled by the Yankees through 2019, but he’s averaged a hair less than five innings per start this year — a troubling trend.

Even in his three straight wins prior to Wednesday, Gray didn’t go past six innings.

“To throw him back out there now might have been a tough hurdle to overcome,” Boone said.