SEATTLE -- The Big Maple is returning to the Mariners. James Paxton tweeted Sunday that he is "super excited" to rejoin the franchise with which he started his professional career.

Paxton agreed to terms on a one-year deal with Seattle for the 2021 season, a source told MLB.com on Saturday. The club announced the deal on Thursday.

Paxton, who was drafted by and spent six seasons with Seattle from 2013-18, will earn $8.5 million in salary, with performance incentives that could take his deal to $10 million based on the number of games he pitches, a source told MLB.com’s Mark Feinsand. That makes the deal a big win-win for both sides in many ways.

Here’s why for Paxton: For all of his accolades as a top-of-the-rotation-type starter, the 32-year-old has battled significant injuries throughout his eight-year career, including a left flexor strain last season and back surgery last February. A one-year deal allows him to re-establish his value and re-enter the market next offseason with the chance to net a longer and richer deal if he can show he’s healthy and effective.

And for the Mariners: They acquire a big upside arm that can potentially eat some much-needed innings and bridge to their younger arms, who will have workload limitations and the burden of ramping back up to a 162-game season. They also bring in a veteran who has since gained postseason experience while pitching for the Yankees, valued veteran experience that could be huge for their young nucleus.

The Mariners have had their eyes on Paxton all offseason, and they were among 20 clubs that watched the lefty throw a bullpen session in Bellevue, Wash., around Thanksgiving, according to MLB.com’s Jon Paul Morosi. Paxton, who averaged 92.1 mph on his fastball in 2020, down from 95.4 mph in ’19, was hitting 94 mph that day. He also drew interest this offseason from the Blue Jays, and he was linked to the Phillies, Cardinals and Mets.

Paxton should slot into the No. 2 spot in the Mariners’ rotation, behind Marco Gonzales and ahead of Justus Sheffield, who was the prized return in the very trade that sent Paxton to the Yanks in November 2018. That deal in many ways sparked the Mariners’ current rebuild, as it was the first major trade by general manager Jerry Dipoto in what has since been labeled the “step-back” offseason.

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After the Paxton domino fell, Seattle dealt Edwin Díaz and Robinson Canó to the Mets in a blockbuster that brought back No. 1 prospect Jarred Kelenic and Justin Dunn, who will enter camp competing for a back-end spot in Seattle’s rotation, which the front office has said will feature six pitchers instead of the standard five. It’s unclear if acquiring Paxton will impact those plans, but most likely not.

At his best when healthy, Paxton has been one of the top left-handed starters in the American League, with a career 3.58 ERA and 114 ERA+. His pinnacle came on May 8, 2018, when he threw a no-hitter for the Mariners against the Blue Jays in his homeland of Canada.

But he’s never pitched more than 160 1/3 innings in a season or reached the 30-start plateau, and he’s been limited to 20 or fewer starts in all but three seasons, including just five in the shortened 2020 campaign. He’s been on the injured list for knee, back, pectoral, elbow and latissimus dorsi injuries dating back to ’14.

That’s why Paxton’s bullpen session in November was significant. Tigers left-hander Matthew Boyd, a Seattle-area native who has been working out with Paxton this offseason, told MLB Network Radio recently that “whoever gets him is going to get a steal.”

“And he’s pumping the ball right now, too,” Boyd said. “He looks better than he ever has. We dove into some stuff, breaking down fastballs and understanding spin direction and all that. His ball just takes off. It’s fun to catch. … Whoever gets him, they’re getting an ace.”

Paxton represents the second significant acquisition by Seattle this week, after the club agreed to terms with closer Ken Giles on Thursday. Giles is recovering from the Tommy John surgery he underwent in October, which will keep him sidelined for all of 2021. But Saturday’s move is much more for the now, and it’s yet another sign that the Mariners are attempting to step forward.