SEATTLE — The Mets completed phase one of what they hope is a rapid retooling of the roster, dealing closer Addison Reed to the Red Sox before yesterday’s 4 p.m. non-waiver trade deadline for three hard-throwing pitching prospects.

In exchange for one of the top relievers in the majors, the Mets got righthanders Jamie Callahan, Gerson Bautista and Stephen Nogosek. All three ranked among Boston’s top 30 prospects, according to MLB.com.

Trading for prospects was not a fate the Mets anticipated when they began the season with high expectations. The deal capped a critical period as general manager Sandy Alderson attempts to get the franchise back into contention next year after a season of unmet expectations.

“We’re pleased with how things developed and turned out over the course of the week,” Alderson said.

Last Thursday, the Mets traded first baseman Lucas Duda to the Rays for Drew Smith, a hard-throwing Double-A pitching prospect. On Friday, the Mets made an unusual move, trading a pair of prospects to the Marlins for closer AJ Ramos.

The deal was made primarily to bolster the bullpen for 2018. Ramos is under team control for next season, when he’ll be expected to help fill the void in the bullpen left by Reed’s departure.

The Mets had hoped to move infielder Asdrubal Cabrera and outfielders Curtis Granderson and Jay Bruce, but they came away with no viable deals. All three, along with second baseman Neil Walker, will be candidates to be traded in waiver deals, which teams can make through the end of August.

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Said Alderson: “We really did not come close to moving any of those players.”

In the case of Bruce, a reunion seemed more possible yesterday, as Alderson said he could envision Michael Conforto sticking in centerfield. Such a move would open a spot for a corner outfielder, perhaps opening an avenue for Bruce to stay past this season.

“We’ve really from the get-go been pretty happy with the way Michael has played centerfield,” Alderson said.

When Reed was acquired from the Diamondbacks in an August 2015 waiver trade for a pair of relief pitchers, the acquisition was somewhat of an afterthought, but he enjoyed a career renaissance during his tenure with the Mets.

Reed, 28, who will be a free agent at season’s end, has a 2.57 ERA with 19 saves in 21 chances in 48 games this season. In 2016, he delivered one of the best seasons by any reliever in the National League with a 1.97 ERA in 77 2⁄3 innings.

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Reed, who had been the Mets’ setup man,, spent most of this season in the closer’s role because Jeurys Familia’s season has been shortened by a domestic-violence suspension and surgery to repair a blood clot.

After the Mets used mostly pitching prospects to swing major deals at each of the previous two trade deadlines to acquire Yoenis Cespedes and Bruce, yesterday’s trade of Reed furthered an effort to restock the farm system with some much-needed power arms. They brought back three intriguing prospects who have a chance to become major-league relievers.

Callahan, 22, is the closest of the three to reaching the majors. Ranked No. 23 in the Red Sox system by MLB.com, the righty had a 4.03 ERA in 22 appearances for Triple-A Pawtucket. He was taken in the second round in 2012 and is considered a project by some scouts but has thrived since his conversion to relief work.

Nogosek, 22, was chosen in the sixth round of last year’s draft and features a fastball, slider and splitter that has gotten swings and misses. Boston’s 18th-ranked prospect had a 4.08 ERA for Class A Salem this season.

Bautista, 22, has a fastball that has been clocked in the range of 96 to 99 mph, with a good slider as his secondary offering. Boston’s 28th-ranked prospect had a 5.16 ERA for Salem.