The Mariners and Yankees came together to complete the first major trade of the offseason on Monday, when Seattle dealt ace James Paxton in exchange for Justus Sheffield, right-hander Erik Swanson and outfielder Dom Thompson-Williams.
That the Mariners landed Sheffield, MLB Pipeline's No. 31 overall prospect, for Paxton, given the latter's age (30) and injury history, is in itself a coup for the organization. The 22-year-old left-hander immediately ranks as the Mariners' new top prospect and represents a possible long-term rotation piece that the club can build around.
In Swanson and Thompson-Williams, the Mariners get a pair of slightly older but still under-the-radar prospects who, after being overshadowed and buried in a deep Yankees' system, both have a real chance of at least becoming Major League contributors, perhaps even more.
Sheffield made his big league debut with the Yankees last September, pitching in three games out of the bullpen after making a late-in-the-season move from the rotation to the 'pen on a temporary, as-needed basis. He posted 1 2/3 scoreless frames between his first two outings in the Majors, but gave up three earned runs on two hits and two walks in one inning in his final appearance.
With the Mariners, Sheffield will now have the freedom to once again develop as a starting pitcher -- only this time he won't have to worry about performing in a short-term role (while also being at the center of seemingly every trade rumor).

Ranked by MLB Pipeline as baseball's fourth-best left-handed pitching prospect, Sheffield is the type of top-tier quality pitching prospect any rebuilding club would want back in such a headline-grabbing trade given his upside as a Nos. 2 or 3 starter. It's precisely why the Yankees targeted him in the deal that sent Andrew Miller to Cleveland in July 2016, two years after the Indians had selected Sheffield in the first round.
Making 21 starts last season between Double-A Trenton and Triple-A Scranton/Wilkes-Barre, Sheffield posted a 2.48 ERA with 116 strikeouts and 50 walks over 108 2/3 innings, during which he held hitters to a .196/.286/.290 clip.
Sheffield's ability to shut down hitters, despite some obvious control problems, speaks to the quality of his stuff.
He's capable of missing bats with all three of his pitches, each of which earns at least plus grades when it's at its best. His fastball has been up to 97 mph in short bursts but as a starter sits at 94-95, with late run and sink. His mid-80s slider can be an out pitch against hitters on both sides of the plate, and his changeup, though on the firm side at times, plays nicely off his fastball, registering in the mid-80s.
Sheffield detractors (i.e., those who already view him as a long-term reliever) wonder whether he will ever learn to harness his impressive stuff well enough to turn over Major League lineups teeming with right-handed hitters. There also are the usual scouting concerns about him being undersized, as a 6-foot lefty.
However, Sheffield's track record during his relatively quick rise through the Minors does highlight a capacity to make adjustments, and he should now have the necessary time and support with the Mariners needed to develop and refine his craft.
Formerly No. 22 on the Yankees list, Swanson -- originally an eighth-round Draft pick by the Rangers in 2014 before they traded him to New York for Carlos Beltran at the 2016 Deadline -- jumps to No. 9 on Seattle's freshly updated Top 30. Though very much a prospect, the 25-year-old right-hander needed to be added to the Yankees' 40-man roster by Tuesday's deadline or be eligible for the Rule 5 Draft.
Splitting much of the 2018 season between Double-A Trenton and Triple-A Scranton/Wilkes-Barre, Swanson pitched to a 2.66 ERA with 139 strikeouts and 29 walks in 121 2/3 innings (24 games, 22 starts). The 6-foot-3, 235-pounder limited opposing hitters to a .210 average.
Swanson has a deceptive delivery that leads to a lot of bad swings against his fastball, which sits at 92-94 mph and touches 97. He leans heavily on his heater, relying on its running action to slip it by hitters up in the strike zone. He has scrapped a curveball and switched to a mid-80s slider than can be a solid pitch at times. His changeup has similar velocity and has become more effective as Swanson has trusted it more.
Swanson has a long track record of throwing strikes, with a career strikeout-to-walk ratio of 354-to-87 in 357 innings across parts of five seasons, though his command isn't as sharp as his control. Improvement on that front, along with the refining of his secondary pitches, could make Swanson a No. 4 starter, or at the least a fastball-heavy reliever.
Thompson-Williams, 23, checks in as the new Mariners' No. 14 prospect and has a big up arrow next to his name entering 2019 after hitting .299/.363/.546 with 22 home runs (tops in the Yankees system) and 74 RBIs over 100 games during a breakout season, much of which he spent at Class A Advanced Tampa. He also stole 20 bases, earning him distinction as one of six Minor Leagues to finish 2018 with at least 20 homers and 20 steals.
Thompson-Williams's power-speed combo highlights what is an intriguing blend of tools, four of which grade as average of better. He has above-average raw power from the left side of the plate that he can get to in games, but questions remain about his ability to make consistent contact and hit for average against advanced pitching, especially after he struck out at a near 25 percent clip during his first full season.
Thompson-Williams's above-average wheels enable him to impact games on the basepaths and in center field, where he's an above-average defender with average arm strength. Those defensive qualities, as well as any contributions at the plate, in turn give Thompson-Williams real big league value to the Mariners as a potential fourth outfielder. Possibly even more, depending on his remaining development.
What's more, before going to the Yankees in the fifth round of the 2016 Draft out of South Carolina, Thompson-Williams was Swanson's teammate at Iowa Western Community College in 2014, when the school won the Junior College World Series.
Sheffield should be the first of the Mariners' new prospect trio to reach the Majors in 2019, though not before checking the necessary developmental boxes as a starter. Swanson could be on a similar timeframe, too, after being added to the club's 40-man roster.
Thompson-Williams has more hurdles to clear in his development than the two pitchers, but as a toolsy, late-blooming position player, his progress also could come more quickly as he adjusts to the game.