Seranthony Dominguez’s move to the Seattle Mariners was supposed to give him a clean slate. Instead, his first outing in Seattle turned into a nightmare.
The former Toronto Blue Jays reliever, acquired by the Mariners from the Chicago White Sox ahead of the 2026 MLB Trade Deadline, was part of the package the White Sox sent to land star pitcher Luis Castillo. Chicago’s decision to move Dominguez wasn’t exactly a shock. He had struggled this season, putting up a 3.99 ERA across 43 appearances while trying to justify the two-year, $20 million deal he signed last offseason.
That rough stretch followed him straight into his new uniform.
Dominguez debuted for Seattle earlier this week against the Detroit Tigers, and the line was brutal: 0.1 innings pitched, two walks, two home runs, four hits, and four earned runs. It was the kind of appearance that leaves no room for debate about how the night went.
Seranthony Dominguez’s first game with the Mariners.
0.1 IP, 4 H, 4 ER, 2 BB, 0 K
2 home runs allowed. pic.twitter.com/LNFaLUZWC5
- Mike (@ChiSoxFanMike) August 5, 2026
Still, there’s a reason the Mariners took the shot. Dominguez showed last season that he can still be a useful late-season arm.
After arriving in Toronto from the Baltimore Orioles, he logged a 2-1 record, a 3.00 ERA, and 25 strikeouts in 24 regular season appearances for the Blue Jays. He carried that into October as well, going 2-0 with a 3.18 ERA and 10 strikeouts in 12 playoff appearances.
Seattle will be hoping that version of Dominguez shows up again down the stretch. The Mariners are three games behind the Houston Astros in the American League West and still pushing to climb the standings.
For now, though, the debut is one Dominguez will want to put behind him quickly.
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